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Monday, October 02, 2017

Annother observatonal epidemiolgic study wiill not settle the issue of the exercise cardiovascular mortality relationship.

There is no debate about the general  nature of the relationship between  regular exercise and cardiovascular risk  and even over-all mortality. As exercise levels ( duration,or frequency or intensity ) increases  the CVD risk decreases i.e there is an inverse relationship.

Controversy exists,however, about  1) whether there is a point beyond which  CVD risk is no longer reduced ( does the curve slope up?) and 2) is there a point beyond which there is actual harm

 The general point that exercise is inversely related to  decreased CVD risk is more than generally accepted even though all the data as regards primary prevention is observational There have been and never will be any randomized clinical trials ( However, there is RCT evidence that a cardiac rehab exercise program will decrease CVD mortality).

In recent years concern has been expressed concerning cardiac problems in  endurance athletes including increased risk of atrial fibrillation, and  the development of areas of cardiac fibrosis ( detected on gadolinium scans)  which have been reputed to   predispose to rhythm disturbance and abnormalities of the right ventricle resembling an genetic condition known as ARVD (arrhythmogenic right ventricular dysplasia).  These and possibly other heart conditions might provide a possible mechanism(s)  responsible for a purported U shaped curve describing cardiovascular mortality and exercise level.It should be noted that there is conflicting evidence as to the shape of this curve, i.e. inverse or u shaped and it is easy to reference a number of studies that support either proposition.The strongest evidence- in regard to the claim that "too much" exercise is harmful- is for the relationship between endurance exercise and atrial fibrillation but even  in  this regard  data also conflict.

Dr. James Okeefe along with Dr. Carl Lavie and others have written extensively  and  often spoken about the hazards of too much exercise and have recommend that relatively low levels of aerobic exercise are adequate to decrease cardiovascular risk.Low levels of exercise have been associated with significance reduction in CVD In fact, simply standing for greater than 2 hours per day is said to be associated with a 10% decrease in all cause mortality - a claim that strains credulity.

Dr. BD Levine from Southwestern Medical school has provided evidence that higher levels of exercise than the currently recommended levels not only protect against coronary  artery disease but can also provide some protection  of the age associated loss of ventricular compliance which arguably predisposes to  heart failure with preserved ejection fraction. (HFpEF) also known as diastolic heart failure. Other workers at the same  institution have recently provided some epidemiological proof of that concept.  Levin has argued that levels of exercise higher than the current recommendation but significantly lower that that practiced, for example by iron man triathletes,will importantly help maintain good left ventricular function and perhaps  ultimately favorably impact  the current "epidemic" of HFpEF.

Eijsvogel et al have provided evidence that the current recommendation regarding exercise to prevent cardiovascular risk may be too low as far as prevention of heart failure (HF) The current (2008) recommendation are for 2 1/2 hours of moderate or one hour and 15 minutes of vigorous exercise per week. (I am reminded of John Von Neumann 's quote " There's no sense in being precise when you don't even know what you're talking about")

Eijsvogel's article defines moderate as 3- 5.9 METS of energy expenditure and vigorous as greater than 6 METS.

For point of reference, running a fifteen minute mile requires about 7 METS ( 24.4 02 uptake) which is equivalent to the 02 requirement for completing Stage 2 of the Bruce protocol. About 5 METs are  needed to finish stage 1 ( 1.7 mph at 10% grade) . Running at  5 MPH or a 12 minute mile requires 8.6 METS. Running 4 MPH require a 02 uptake of about 25 ( 7 METS)

A sometimes used  prediction equation that approximates a person's maximal 02 uptake is 3.8 times how long in minutes the person could preserver  on the Bruce treadmill protocol.

Eijsvogel and co-workers used the data from the work of Wen and Tsai and of Arem  to construct a cardiovascular disease mortality -physical activity curve .  and found the "sweet spot" of  41 MET hours per week or 2460 METS hours per week The sweet spot  ( not their term) means the level of exercise at which the maximal benefit in terms of reduction of CVD risk is reached.

This corresponds to 9 hours of walking or 4.8 hours of running at a 12 minute mile.

This is 3 to 4 times higher than the widely quoted 2008 recommendations of 2.5 hours of moderate or 75 minutes of vigorous exercise per week.

Another study  by Lee et al also derived a activity CD risk relationship curve and found a lower sweet spot.

So the sweet spot from Lee's data is run for 3.5 hours  per week versus 4.8 in Eijsvogel's article. O'Keefe seems to rely on Lee's data when he recommends for one to "limit one's vigorous exercise to 30-50 minutes a day. Not every one would consider running 3 1/2 hours per week at a 12 minute per mile pace a small amount of exercise and this would represent about 2- 3 times the 2008 recommendations and accepting Levine's thesis would be sufficient (if done for many years) be enough to decrease not only te risk of CVD is general but also the risk of developing heart failure with preserved ejection fraction (HFpEF).

But what will happen in terms of cardiovascular harm if you exceed the fifty minutes per day recommended by Okeefe and Lavie.From reading  Eijsvogel's analysis- my sense of is , not much. His group was unable to show an increased CV risk at any level though using some parameters of exercise intensity or duration the curve sloped up slightly at the far right but was not statistically significant.

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