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

Playing at Evolution

UHeart

Picture taken from www.blogs.simplyfun.comTake a look at children playing, and undoubtedly you’ll smile at their innocence and fun. But did you know the evolution of humanity depends on this seemingly unstructured playtime?  Researchers now postulate that the ability of human children to play has differentiated us into a unique species that can actively manipulate and change our environment.

As David Dobbs of the NY Timeswrites, “Other species play, but none play for as much of their lives as humans do, or as imaginatively, or with as much protection from the family circle. Human children are unique in using play to explore hypothetical situations rather than to rehearse actual challenges they’ll face later.”

The article goes on to demonstrate the innovative work of Dr. Alison Gopnik, who has shown that children are actually quite expert at exploring their environments without prior bias or reliance on the safer, high-probability choices. By contrast, adults lose…

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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

Caffeine For Strength Training: A Review and Opinion

Much has been researched on the beneficial effects of caffeine for endurance/aerobic training. There are too many articles supporting these claims to make listing them reasonable. There is a reason why the IOC, NCAA and USTAF have strict restrictions and blood testing protocols for caffeine; it simply works. The rationale behind this is that caffeine helps facilitate free-fatty acid metabolism preferentially over glycogen and other carbohydrate homologs in the body. Fat generates a higher yield of ATP with a subsequent lower production of lactate, which is needed in long duration aerobic exercises. In addition to these metabolic effects research has shown caffeine to provide a temporary analgesic effect, which is extremely beneficial to endurance athletes during the final legs of their races when they are pushing themselves and likely utilizing anaerobic systems which can be painful. Cyclists have realized this analgesic effect for years as they used to fill their water bottles during races with flat cola. in addition to these effects, caffeine is a brochiodilator and also allows the diaphragm to contract more forcefully this is why pulmonary therapists administer caffeine to patients prior to treatment.

In a review published by McCormack and Hoffman in this July’s Journal of Strength and conditioning they highlight the potential benefits caffeine may provide for power and strength training. The mechanisms they attribute to the positive effects caffeine may provide are neuromuscular and central nervous system mediated. The CNS effects are founded under caffeine’s stimulant properties by blocking adenosine receptors which alters the perception of fatigue, improves focus and reaction time. Due to these effects, caffeine has been used as an alternative to amphetamines in USAF pilots flying repeated missions who require the mental acuity and sustained reaction time to complete a tactical flight operation.

The neuromuscular effect is mediated by enhanced excitation-contraction coupling through the Treppe effect. The treppe effect improves neuromuscular transmission by increasing the mobilization of intracellular calcium ions from the sarcoplasmic reticulum which is required in for the cross bridging between actin and myosin heads which produce a muscle contractions. Caffeine is also thought to enhance the kinetics of glycolytic regulatory enzymes, which are active in strength training activities, such as phosphorylase. The results of these metabolic and neuromuscular effects appear to allow the muscle to not only produce a more forceful contraction but also increase the number of repetitions per set. There have also been studies that have found caffeine if ingested acutely after a bout of exercise, (in the highlighted study’s case it was short duration high intensity intense cycling) recovery had improved as compared to a placebo on a quadriceps strength test.

Though the authors did report evidence that caffeine ingestion may be beneficial for strength and power training it appears though that the results are inconclusive as to whether or not caffeine in isolation results in these effects. The majority of these studies administered caffeine in the form of an energy drink or some sort of caffeine-proprietary nutrient concoction. The most common additives are taurine, beta-alanine, creatine and other amino acids; all of these supplements have shown to improve recovery and endurance to varying degrees. There also appears to be a dosage effect as well as most of the studies that resulted in improvements administered caffeine at the dosage of 5-6mg/kg body weight. Which if you consider that per 8oz of liquid redbull contains 80mg, coffee contains 110-150mg, and cola contains 30-40mg; so you may have to consume a considerable amount to get these effects much more than most have ever consumed.

Although these results are encouraging for the usage of caffeine for strength training purposes, in my professional opinion I would tread with caution. Caffeine can be rather dangerous to someone if administered in these high dosages without proper cardiovascular testing. Caffeine is sympathomimetic drug, which means it provides effects similar to those caused by the sympathetic nervous system which will increase HR, BP and blood flow to the skeletal muscle, amongst other effects. If someone who had an undiagnosed problem or defect were to ingest caffeine with these recommended dosage rate serious problems could occur. So it would be best to consult your physician before initiating a dosage regimen and have a physical therapist monitor you the first few times you exercise to monitor for deleterious effects/changes. Secondly, though the authors sited evidence of improved strength and power upon further review of the literature a lot of the studies they cited had subjects exercise to exhaustion or tested them on isokinetic strength tests. Tests to exhaustion are not a reliable or valid measure of strength or power and isokinetic testing does not assess the patient in functional movement pattern or at an angular velocity consistent with normal movement. In summary the evidence isn’t that strong to suggest direct strength and power gains but it may improve both factors in an indirect way, which I will elaborate on.

As most people in the field of sport performance and nutrition know most of the focus for supplementation is focused around recovery. Caffeine does directly improve recovery probably due to the increased, cardiac output and perfusion to the skeletal muscle. These cardiovascular effects will help remove metabolic waste products away from the muscles to the liver and help bring nutrients to the muscle. The authors however did not mention the benefit of caffeine as a moderate bronchodilator on training. If the bronchioles are more dilated it will improve ventilation to help buffer out the drop in ph due the shift in the strong ion difference following an acute bout of exercise. Similar to other supplements caffeine does show to improve the amount of repetitions a person can perform due to the previously mentioned improved blood flow and analgesic effect. If someone can decrease the soreness they feel during a max lift or increase the amount of repetitions they can perform, strength will improve over time.

In short caffeine like many other supplements helps you work out longer through it’s metabolic, cardiovascular, neuromuscular and central nervous system effects. It helps improve muscle metabolism by improving blood flow to the muscle, ventilation, focus and decreases pain. Dosage should be close to 5-6mg per kg body weight and administered 45min prior to exercise or immediately after.

Thanks for reading!

Here is a link to the article

http://journals.lww.com/nsca-scj/Abstract/2012/08000/Caffeine,_Energy_Drinks,_and_Strength_Power.3.aspx