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.

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