On Logical Fallacies

Webcomic_xkcd_-_Wikipedian_protester

 

Popular opinion ≠ truth. Stating that a source’s credibility is enhanced by its popularity is a logical fallacy (argementum ad populum). Another important fallacy to avoid is the notion that the duration of how long an idea has been accepted reflects its validity (argumentum ad antiquitatem). The notion that something is true because it can’t be observed to be false (argumentum ad ignorantiam and argumentum ex silentio) should also be avoided. A few things to think about in regards to clinical decision making and practice.

I think we fall victim to these fallacies and others more often than we should, not necessarily with malicious intentions. Humans are creatures of habit and will often reflexively attempt to simplify complex topics and concepts to fit a narrative and world view. I am guilty of this as well, we all have our biases. However realizing this and taking time to think “why do I perform or choose the things that I do” is important to prevent this from perpetuating and having too strong an influence over one’s decisions. Remember the truth defies simplicity.

On clinical approaches

mind-tricks

Image Coureousy of Theo Lister lifehack.org

 

Do we often over complicate things with our approach to the rehab of MSK disorders? I, likely more than most, firmly believe in the concept “the truth defies simplicity”; however often the causative factor for a problem is rather apparent with an equally simple solution. Too often do I observe approaches based on loose scientific principles or over extensions of human physiology. These behaviors often obfuscate thinking and make treatment more complicated than it should be. The understanding or perception regarding the attributed mechanism for an intended therapeutic effect is important; for both provider and patient. In short, why is as important as what is done or chosen for treatment. Granted there will be variability in approaches based on one’s training and knowledge base; but are our thoughts often too scattered and random when they should be more focused and directed? Does this uncoordinated way of thinking impact our outcomes? Does this matter? Let’s hear your thoughts (pun intended).

On Preventative Physical Therapy

I have encountered a few discussions recently regarding the implementation of an annual physical therapy exam. The original source of this thought likely traces back to the legendary Shirley Sahrmann who has talked at length about this concept. The foundation of the argument appears to stem from the belief that preventative medicine is cost effective (which it is) and that physical therapy improves outcomes at a reduced cost (which it does for a lot of reasons and disorders). While both of these aspects are fairly valid, combining them to suggest that everyone would benefit from seeing a physical therapist (or any provider) annually and that this exam would reduce healthcare costs is a bit of a stretch.

First, we also need to acknowledge that the term “preventative” medicine is a slightly inaccurate. No disease or injury can truly be “prevented”; despite optimal care and an ideal patient, there will always be some risk. For movement based disorders physical therapy services can absolutely reduce risk and improve performance in many domains. We should also continue to screen for systemic disease. However labeling what we offer as prevention may create unreasonable patient expectations and unrealistic beliefs in a providers utility. Both of which can influence outcomes. But for now, until we devise a better word we’ll go with “prevention”

For most healthy individuals, receiving an annual physical therapy examination would be meaningless and it would come at cost. If an individual moves well and is disease free there are few benefits to them receiving examinations by a PT (or any provider) annually. This is similar to the issue encountered with the overly-capricious use of diagnostic imaging. If the pre-test probability is low then the test/image isn’t going to be useful and may result in false positives (See Bayes’ Theorem of conditional probability). Which leads to more testing, clinical visits and further costs. This issue occurs with imaging and tests that actually possess strong statistical power, which many of our movement based exams lack. Thus the false positive rate for an annual physical therapy exam may potentially be even worse!

We also must consider the bio-psychosocial ramifications associated with these potential false positives. One of the issues with over-utilization of imaging is that provides a tangible “proof” to patients that they are “broken” and often remain attached to those results. It can be quite difficult to break that cycle once it starts. Another example of this are those who visit a chiropractor monthly ad infinitum for tune-ups. What is actually being improved and is manipulation necessary even if the technique results in cavitation? Most (rightfully) would consider the notion of regular chiropractic visits to be unreasonable. Seeing a physical therapist annually despite being asymptomatic would be as well.

Even the utility of annual medical exams/physicals have even been investigated recently. With the majority of the evidence suggesting that they may actually increase costs without reducing much risk. This further analysis of risk reduction is also likely why the ACSM has recently adapted their recommendations and removed ETT/medical exams for many patients even those with risk factors. The old ACSM guidelines created bottlenecks in access to care, and delayed the initiation of exercise which affected outcomes. With the provider gap that currently exists in this country, the delivery of care needs to be as efficient and effective as possible. Annual visits to a physical therapist could also potentially impair access to care for those most in need of rehab services.

When deciding on policy change it must always be asked, does the intervention reduce risk and associated healthcare costs more than the cost of providing it? While I agree that access to physical therapy services needs improvement this annual model needs to be further analyzed. I suggest that maybe a “regular” physical therapy exam combined with other providers should be implemented. The frequency of this exam could then be modified based a number of health-related factors (congenital diseases, family history) and adapted to any novel changes (weight changes, acute injury etc). From our end we also need to start tracking outcomes data more consistently to help improve the effectiveness and efficiency of our care (which I have been working on improving with my software “Outcome Manager” set to release in the coming months) and develop more accurate tests and measures.

Again, as always the truth defies simplicity.

On Crossfit

crossfit-fuengirola-slide03

 

I wish more PT/physios would realize the potential in owning a box or gym and operating a clinic contained within. Instead of commenting on the issues with training and programming that Crossfit or any other training model has, we should be looking at ways address them while incorporating them into practice models. I’m more of an academic at this point in my career (and likely going forward) but it would seem that having a more fit and motivated patient population would be ideal. Having multiple revenue streams, a greater potential for direct access and collaboration with fitness professionals to ensure a smooth transition post rehab are all decent perks; not only for clinicians but patients too. These are all items that are frequently mentioned as lacking in most clinical models and barriers to outcomes. Why more of us haven’t explored this business model is beyond me and appears to defy logic.

The primary point I am getting at is that owning a gym, box, Pilates studio, fitness centers etc should not be the exception rather the norm. As would owning your own clinic vs working for one of the large PT chains. We complain about revenues and reimbursement, yet we as a profession choose to work in situations where our earnings are limited with sometimes ridiculous work demands and paltry compensation. What other profession practices in this manner?  Of course there is significant capital required to operate your own business with increased risk, especially early in one’s career. But this sort of model is ideally developed over time and possibly in partnership with a few like-minded clinicians (not necessarily PTs) to divide the risk. At the end of the day one will never earn as much as they can working for somebody else. Until we as a profession realize this, from a practice standpoint we will continue to remain significantly impaired in our ability to move forward.

The Oxygen Delivery Problem

For those working in acute or cardiopulmonary sections of physical therapy you may have considered this:

“If a patient has a low oxygen saturation and they respond to supplemental oxygen why don’t we just put them on a non rebreather mask non-stop? It would surely provide them with enough oxygen that they would never desaturate”.

A non-rebreather mask (NRB)

A non-rebreather mask (NRB)

For starters a non rebreather mask (NRB) is an oxygen delivery device that provides patients with a fraction of inspired oxygen (FiO2) of 100% and is used on patients in critical conditions such as ARDS . Normally the air we inspire is a mixture of gases, mainly nitrogen (78%), and the FiO2 is 21%. The amount of both gases in this mixture is important physiologically for a number of reasons. Due to the increased affinity of hemoglobin for oxygen at the alveolar level due to the Haldane effect (also see Bohr effect transport of O2 to working tissue) oxygen is preferentially absorbed over other gases and nitrogen remains in the lungs which help maintain the inflation of the alveolar sacs. If one were to increase the percentage of inspired O2, over a period of time there would be less nitrogen available to maintain the patency of alveoli. Due to the physiological principles described above this would eventually result in alveolar collapse or the technical term “absorption atelectasis

Secondly, increased blood levels of O2 can suppress the ventillatory drive, especially in patients with Chronic Obstructive Pulmonary Disease (COPD) who demonstrate CO2 retention(1-2). CO2 retention, defined as increased blood gas values of CO2, can occur in patients with severe COPD (1). The mechanisms for this physiological process are still not completely understood. Carbon dioxide values, in a normal functioning system, regulates the drive to breath, via central and peripheral chemoreceptors (3). In patients with CO2 retention this mechanism is altered and their body responds to circulating levels of oxygen; lower levels of O2 facilitates breathing and higher amounts suppress (1-3). Therefore increasing the amount of delivered oxygen to a patient with this condition could possibly result in apnea.

Hyperoxia (higher than normal levels of oxygen) has also been shown have other systemic effects on the body (4-7). In the peripheral vasculature, hyperoxia causes vasoconstriction. The amounts of vasoconstriction and blood flow reduction varies in body area as the coronary arteries and brachial arteries demonstrate markedly reduced blood flow when exposed to hyperoxic states, the reduction in the cerebral arteries appears to be less (5-7). In addition to the vasoactive effects, hyperoxia can also lead to an increase in reactive oxygen species which can lead to oxidative stress and damage tissue (7).

Rarely does one chemical, tissue or system act completely in isolation. Your body is not a petri dish and we do not operate in a vacuum. The effects from something seemingly innocuous to one organ system may result in deleterious effects to another. Just because the reaction in a cell to a given amount of substance is beneficial is does not always mean that more of that chemical is always good. Human physiology is a story, with many subplots and characters with an exer-expanding number of volumes as we learn more about the body.

1 Kim S et al, Oxygen Therapy in Chronic Obstructive Pulmonary Disease Proc Am Thorac Soc. May 1, 2008; 5(4): 513–518. source 

2 Gorini M et al, Breathing pattern and carbon dioxide retention in severe chronic obstructive pulmonary disease Thorax 1996;51:677-683 source 

3 Jones and Barlett Learning LLC 2014, Regulation of Ventilation pgs 4-14, source 

4 Dean J et al, Hyperoxia, reactive oxygen species, and hyperventilation: oxygen sensitivity of brain stem neurons, J Appl Physiol 96:784-791, 2004 source 

5 Farguhar H et al, Systematic review of studies of the effect of hyperoxia on coronary blood flow, Am Heart J. 2009 Sep;158(3):371-7 source 

6 Xu F et al, Effect of hypoxia and hyperoxia on cerebral blood flow, blood oxygenation, and oxidative metabolism. J Cereb Blood Flow Metab. 2012 Oct;32(10):1909-18. source 

7 Rossi P and Boussuges A, Hyperoxia-induced arterial compliance decrease in healthy man, Clin Physiol Funct Imaging. 2005 Jan;25(1):10-5 source.

Pediatric Exercise Testing

Introduction

In the adult population, when a patient sustains a cardiovascular insult requiring surgery or some other form of medical therapy and quite often the patient is referred to cardiac rehabilitation. With increased survival rates following cardiac surgery(1) cardiac rehab is an important component to the overall recovery of the patient by safely returning them to their prior level of function it has also been shown to reduce morbidity, readmission rates and cost (1). An important component to the evaluation process for cardiac rehabilitation is the results from exercise testing. Testing is either performed by a cardiologist before referral or in the outpatient clinic by a physical therapist or exercise physiologist. For adults there are a litany of standardized testing protocols and procedures available to the clinician to use dependent on the case. After finishing a clinical at a Pediatric Trauma 1 hospital where I spent an extensive amount of time treating children with cardiovascular pathologies I began to ask what is the most valid and reliable measure to use for a pediatric population? Similar to adults, pediatric cardiac procedures have improved and patients are living longer(1,2,3). Due to this increased survival rate it would be beneficial to examine the most appropriate functional capacity or exercise test for pediatric patients as the goal of allowing the patient to perform activities at their highest level of functional independence is similar but the hemodynamic response to exercise, gait mechanics, respiratory mechanics are different from adults and amongst different ages of children.  From what I gathered from staff members is that many are not sure either. This post will evaluate  two of the most commonly used exercise tests for pediatrics patients, the Bruce Protocol and 6 minute walk test. The benefits and limitations will be provided for each test as well as a summary and recommendation for clinical implementation.

Bruce Protocol 

The Bruce Protocol is a progressive graded treadmill test. The standard protocol consists of  7 stages, each lasting three minutes. The test can last up to 10 stages though most patients don’t surpass stage 6. The test starts with having the patient walk at 1.7 mph (2.7 km) up a 10% incline and after each 3 minute stage both the treadmill speed and incline are increased according to the protocol (Figure 1). Heart rate, EKG and Respiratory rate are constantly assessed, rate of perceived exhaustion (RPE) is taken every minute, blood pressure is taken after each stage. The patient’s VO2max is then determined either by using a regression plot based on the stage the patient completed (if the test was not a true max test), vitals response and body-weight or gas exchange analysis (Figure 2) (if available at the facility).

Figure 1.

Standard Bruce protocol

Standard Bruce protocol

Figure 2.

treadmill test

A patient performing the Bruce Protocol

Benefits of Bruce Protocol for Pediatric Patient 

The Bruce provide a more accurate assessment of cardiovascular system’s function, more specific information on what caused the termination of the test, a more accurate estimation of VO2max and constant monitoring of vitals. The test has had gone through countless meta-analyses and systematic reviews examining it’s validity and reliability amongst other measures; established norms have been developed for healthy pediatric populations (4,5).

Limitations of Bruce Protocol for a pediatric patient

The Bruce protocol has some practical disadvantages. For well trained children, the walking speed at the first 4 stages of the Bruce protocol are too slow, additionally the 3 minute duration of each stage is too long which may lead to boredom (5). The most appropriate running speeds for well trained children occur during stages when the elevation is high >18% grade (5,6). Thus the most velocity appropriate stages of the Bruce Protocol occur at relatively steep grades which encourages subjects to hold onto the handrails, thereby affecting the oxygen cost of exercise significantly. Several studies have demonstrated that usage of handrail support increases treadmill time (TT) (7,8), with the largest significant difference occurring when the front handrail is used (7), even  support is limited to 2 fingers it is enough to create a small but statistically significant increase in TT in some patients (7,8). There are separate regression tables and values for handrail usage (7,8). For younger or more limited children, the increase in work increments between successive stages may be too great, resulting in the tendency for subjects to quit during the first minute of a new 3-minute stage (7)

6 minute walk test (6MWT)

The 6 minute walk test (6MWT) is a non graded constant load, constant intensity exercise test used to assess the submaximal level of functional capacity. The test is relatively simple in that it only requires a 100-ft hallway (Figure 3) and no exercise equipment or advanced training to administer it. This test measures the distance that a patient can quickly walk on a flat, hard surface in a period of 6 minutes. It evaluates the global and integrated responses of all the systems involved during exercise, including the pulmonary and cardiovascular systems, systemic circulation, peripheral circulation, blood, neuromuscular units, and muscle metabolism (9,10,11).

Figure 3.

6 minute walk

6MWT course

Benefits of the 6 minute walk test for a pediatric patient

6 minute walk test for children has excellent test-retest re- liability (ICC = 0.94) and moderate yet statistically significant, correlation between 6-minute walk distance (6MWD) and V02 (10) have been reported (r = 0.44-0.73, P < .0001). The 6MWT provides information that may be a better index of the patient’s ability to perform daily activities than is peak oxygen uptake as most activities of daily living are performed at submaximal levels of exertion (12)

Limitations of the 6 minute walk test for a pediatric patient

The 6MWT does not determine peak oxygen uptake as it is by design a submaximal test. It does not provide specific information on the function of each of the different organs and systems involved in exercise or the mechanism of exercise limitation, as is possible with maximal cardiopulmonary exercise testing (9,10,11).Patients who become fatigued are in fact allowed to take a rest break . Some authors argue that the results from a 6MWT should not be used to supplant a formal exercise test (such as the Bruce) however some studies suggest that it is a reliable measure of functional capacity (9-11).  A systematic review evaluating the effectiveness of the 6MWT in pediatric populations published  Physical Therapy and found that there was a large variation in test procedures among the included studies, and only 1 study followed all ATS guidelines (10). In addition to that  having a child “walk as fast as they can without running” is a potential problem in regards to compliance due to patient understanding. That may result in skewed data and other statistical or methodological issues.

Discussion and Summary

The Bruce does provide a more accurate assessment of the cardiovascular system’s function however the testing conditions are not reflective of normal daily physical activity. Due to the lack of instrumentation required, the usage of more normal gait conditions and since most activities of daily living are performed at submaximal levels of exertion the 6MWT appears to the more valid test to assess tolerance to functional activity for this patient population. Although Bruce is more a specific test for cardiovascular function the 6MWT is more valid for assessing tolerance to functional activity. More research is needed to examine the cause for the inconsistencies in administration of the 6MWT.

Cardiac Rehabilitation  in the pediatric population is greatly underutilized, and though clinical research on this aspect of therapy is promising it has been limited (2).  However, a systematic review by Tikkaken et al in 2011 found that the “benefits [of cardiac rehab cardiac rehabilitation in children with congenital heart disease] have been observed in many studies, and no adverse events have been reported”. This is encouraging however with any intervention more evidence needs to emerge to support its implementation.

Works Cited

1) Arena, R Et al Cardiac Rehabilitation Attendance and Outcomes in Coronary Artery Disease Patients, Circulation. July 9, 2012;

2) Tikkanen A et el, Paediatric cardiac rehabilitation in congenital heart disease: a systematic review, Cardiology in the Young (2012), 22, 241–250

3) Algra S et al, Improving surgical outcome following the Norwood procedure, Neth Heart J (2011) 19:369–372.

4) Connor J et al, Clinical Outcomes and Secondary Diagnoses for Infants Born With Hypoplastic Left Heart Syndrome, Pediatrics Vol. 114 No. 2 August 2004

5) van der Cammen-van Zijp, M et al, Exercise testing of pre-school children using the Bruce treadmill protocol: new reference values, Eur J Appl Physiol (2010) 108:393–399

6) Cumming, G et al, Bruce Treadmill Test in Children: Normal Values In a Clinic Population, The American Journal of Cardiology (1978) Volume 41 pg 69-76

7)Berling J et al, The Effect of Handrail Support on Oxygen Uptake During Steady-State Treadmill Exercise, Journal of Cardiopulmonary Rehabilitation 2006;26:391/394

8)Manfre M et al, The effect of limited handrail support on total treadmill time and the prediction of vo2 max, Clinical Cardiology Volume 17, Issue 8, pages 445–450, August 1994

9) ATS Statement: Guidelines for the Six-Minute Walk Test; Am J Respir Crit Care Med Vol 166. pp 111–117, 2002

10) Bartels, B et al, The Six-Minute Walk Test in Chronic Pediatric Conditions: A Systematic Review of Measurement Properties, Physical Therapy. 2013; 93:529-541.

11)Lammers A, et al, Comparison of 6-min walk test distance and cardiopulmonary exercise test performance in children with pulmonary hypertension

12) Geiger R et al, Six-Minute Walk Test in Children and Adolescents, J Pediatr 2007;150:395-9

Shone’s Disease a rare congenital heart syndrome

Shone’ Syndrome

  • A rare congenital heart disease described by Shone in 1963
  • Manifests as decreased left ventricular output
  • There are two types of Shone’s syndrome: complete and incomplete Shone’s syndrome.
  • In the complete form of Shone’s syndrome, all four of the lesions will be present.

In the incomplete form, two or three lesions will be present (more common)

Supravalvular mitral membrane (SVMM): Typically the first abnormality to develop. An abnormal ridge of connective tissue on the atrial side of the mitral valve. Often the supravalvular ring may encroach on the orifice of the mitral valve leaflets and restricts their movements. While a supravalvular mitral ring may allow normal haemodynamic flow from the left atrium to the left ventricle, it often causes an obstruction of the mitral valve inflow(cite). Mitral supravalvular ring is associated with other defects in almost 90% of cases

Valvular Mitral Valve stenosis due to a parachute mitral valve: The mitral valve chordae insert into one papillary muscle. In parachute-like asymmetric mitral valve, most or all chordal attachments are to one papillary muscl. This abnormal attachment of the chordae tendonae results in stenosis of the mitral valve since the valves are held in close proximity.

Subaortic stenosis (membranous or muscular): is a fixed form of anatomic obstruction to outlet of blood across the left ventricular outflow tract. There are four basic anatomic variants which are as follows: (1) a thin discrete membrane consisting of endocardial fold and fibrous tissue, (2) a fibromuscular ridge consisting of a thickened membrane with a muscular base at the crest of the interventricular septum, (3) a diffuse, fibromuscular, tunnel-like narrowing of the LVOT, and (4) accessory or anomalous mitral valve tissue.

Aortic Coarctation: Coarctation of the aorta is a narrowing of the aorta most commonly found just distal to the origin of the left subclavian artery. Since the narrowing occurs distal to the L subclavian artery symptoms typically are manifested in the lower extremities such as cramps, cold feet and decreased ability to perform exercise. Aortic coarctation occurs in 20–59% of cases with mitral valve anomalies

Here is an illustration of the pathology:

Untitled

Associated Pathologies
Heart failure, pulmonary hypertension, pulmonary edema, right ventricular hypertrophy, Left ventricular hypoplasia, pneumonia and cor pulmonale.

Diagnostic Imaging:
Echocardiogram, Pulmonary Artery catherization, MRI, chest radiograph, heart auscultation, EKG

Clinical Exam/Findings:
Loud S2, cold feet, bilateral rales/crackles. Orthopnea, diastolic murmur, atrial fibrillation, low cardiac output,

Prognosis:
If detected early surgery can be performed to correct the defects and is typically done in stages, which reduce dysfunctions. The longer the patient goes untreated and the more elevated pulmonary artery pressure increases the more worse the outcome.

heartbaby

A happy patient post surgery 🙂

Differential Diagnosis:
Tetraology of Fallot, Cor triastrium sinister, patent ductus arteriousum, bicuspid aortic valve

Works Cited

  1. Iwata Y, Imai Y, Shin’oka T, Kurosawa H. Subaortic stenosis associated with systolic anterior motion. Heart Vessels. Nov 2008;23(6):436-9.
  2. Morris et al, CT and MR Imaging of the Mitral Valve: Radiologic-Pathologic Correlation, RadioGraphics, October 2010; 30, 1603-1620.
  3. Otto CM, Bonow RO. Valvular heart disease. In: Libby P, Bonow RO, Mann DL, Zipes DP, editors. , eds. Braunwald’s Heart Disease: A Textbook of Cardiovascular Medicine 8th ed.Philadelphia, PA: WB Saunders; 2007:1625-1712
  4. Bonow RO, Carabello BA, Chatterjee K, et al. 2008 Focused update incorporated into the ACC/AHA 2006 guidelines for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines Circulation 2008;118:e523-e661.
  5. Serra W*, Testa P and Ardissino P Mitral supravalvular ring: a case report, Cardiovascular Ultrasound 2005, 3:19
  6. Popescu BA, Jurcut R, Serban M, Parascan L, Ginghina C. Shone’s syndrome diagnosed with echocardiography and confirmed at pathology, Eur J Echocardiogr. 2008 Nov;9(6):865-7
  7. Board, A.D.A.M. Editorial. Coarctation of the Aorta. U.S. National Library of Medicine, 18 Jan. 0001. Web. 08 Mar. 2013.
  8. Brauner R A, Laks H, Drinkwater DC Jr, Scholl F, McCaffery S. Multiple left heart obstructions (Shone’s anomaly) with mitral valve involvement: long-term surgical outcome. Ann Thorac Surg 1997;64:721-9