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Tuesday, March 20, 2018

If endurance exercise is the fountain of youth how much do you have to drink?

The arc (s?) of the normal aging heart -

One of the stories told  by physiologists and cardiologists regarding the age related downhill course of cardiac function is something like this.

One way to simplify  cardiac function is to consider the two parts of the cardiac cycle,1) contraction and ejection of blood and 2) relaxation and the refilling of the ventricle.

There are data indicating that the first signs of an impending problems are seen in the filling phase ie. diastole.From extensive echocardiographic and invasive physiologic measurements in humans the following sequence can be sketched out.

First there is impaired relaxation following by decreased elastic recoil and later diminished  compliance ( which is to say increased stiffness) and then -at least according to work from the EEM group- remodeling of hearts with thicker walls and smaller ventricular volumes).Simply put a sedentary ageing  lifestyle leads to a small stiff heart and long time endurance exercise leads to a larger more easily filled heart.The contractile function of the heart is well preserved with ageing , at least as indicated by measurement  of the ejection fraction.

This is largely consistent with the mainstream echocardiographic model which proposes a predictable,progressive process beginning with impaired relaxation,followed by decreased compliance and ultimately- as a compensation- elevated filling pressures.This model describes three phases of diastolic dysfunction indentifiable by combination of echo findings believed to reflect  how well or poorly blood flows into the ventricles from the atrium. This model recognizes that the various indices ( e.g E/A ratio, IVRT,maximal E wave velocity and the time constant of isovolumic pressure decay (Tau) change with age so that what would be abnormal in a 20 year old is normal in a 75 year old.It is thought that that filling pressure can be estimated by use of this model. NOTE-see end note 1 for reference to data that challenges the mainstream model by in part  providing data that cardiac cath measurements of left sided pressures do not regularly correspond with the three echo defined stages of diastolic dysfunction)

Now we look at what I have labelled as the "Dallas or EEM theory" of cardiac ageing. see end note 2

A series of articles from the University of Texas Southwestern Medical School and the EEM have provided extensive invasive and noninvasive data regarding cardiac function at various ages and the effect of longtime endurance exercise versus sedentary ageing on  cardiac structure and function.

Levine et al first demonstrated that lifelong endurance athletes ( 25 years or more of running a lot) had left ventricular compliance virtually identical to those of sedentary 20-30 years olds. Then they compared ventricular compliance in four groups of 25 each of people who exercised at various levels over a 25 years period. These were all subjects over the age of 64 and were screened to excluded pre-existing heart disease.Group 1 was sedentary people who exercised no more than one session per week. Group 2 were labelled "causal exercisers" and exercised 2-3 times per week. Group 3 (Labelled as committed exercisers}worked out 4-5 times per week and the "competitive" group trained 6-7 times per week and regularly raced.The racers had the most elastic ventricles while group 3 was "very close" in terms of ventricular compliance while groups 1 and 2 has significantly stiffer hearts.

Next Levine studied a group of 70 year old subjects  and an exercise program was unsuccessful in improving the reduced compliance observed in that group. Next a study was able to show that middle aged subjects with a year long exercise program ( that involved in part high intensity interval training) was able to increase their ventricular compliance.

My main question in this regard is "how much exercise "is sufficient to maintain a healthy compliant left ventricle." Levine's amazingly compliant  (pun intended) subjects not only stuck with program for a full year but after the first 6 months participated in a hig intensity interval program using the 4X4 workout program that involves 4 minutes of exercise at 95% of maximal heart rate followed by 4 minutes of rest done four times.

End note 1. Grant et al (Grant A, Grading diastolic function by echocardiography:hemodynamic validation of existing guidelines.Cardiovascular Ultrasound 2015 513 :28) compared echocardiography results with  left heart catherization data in 460 patients.The data demonstrated that there were no differences in regard to left ventricular pressures between patients with normal diastolic function and those with grade 1 or 2 diastolic dysfunction but there were differences between normal and grade 3 diastolic dysfunction in patients with reduced ejection fraction.In those patients with preserved EF, there is no statistical difference between normal and any grade of diastolic dysfunction. (see figure 5 of their article which graphically illustrates the lack of the "predictable, progressive process "which characterizes the  current paradigm.)If the detection of elevated LV pressures which generally correlates with exertional shortness of breath is in part the goal of echo studies of diastolic function it appears to not be reached based on Grant's data.

end note 2. Dr Ben Levine is the founder and director of the Institute for Exercise and Enviromental Medicine (EEM) housed at the Texas Health Presbyterian Hospital Dallas and professor at University of Medicine Southwestern. His group have done a series of comprehensive physiological studies on subjects recruited from the Dallas Heart Study, a population based sample of 6100 subjects in Dallas .
In a nut shell the concept is that everyone with aging develops some degree of diastolic dysfunction related to impaired relaxation and loss of diastolic suction,Later aging (particularly sedentary ageing) is associated with loss of ventricular compliance ( AKA increased stiffness). A long term endurance exercise program is capable of mitigating the changes in compliance but not the decrement in relaxation and diastolic suction. EEM's studies  further indicate that a sedentary lifestyle may lead to a small stiff heart which may be the precursor to heart failure with preserved ejection fraction (HFpEF) ) and the Dallas group suggest that an appropriated amount of endurance type exercise begun no later than early middle age may play an important role in the prevention of HFpEF.

"Humans are pattern-seeking story -telling animals and we are quite adept at telling stories about patterns, whether they exist or not".Michael Shermer.
In 2008, Shermer coined the term "patternicity" -the tendency to find meaningful patterns in meaningless noise. I am not suggesting that the extensive,very carefully done research referenced above is meaningless noise.I just really like the quote but I certainty hope the "Dallas hypothesis" ( my term) proves to be of significant value, having spent a lot of time running a lot over the years.

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