I don’t know, any one has tried to differentiate the mechansims of dyspnea with reference to systolic and diastolic dysfunction .We have made some observations in certain group of patients during EST . I do not know how far one would agree with this .
For the same amount of stress or work load persons with systolic dysfunction behave differently . However ,both will complete the activity but the onset and perception of dyspnea is slightly different in patients with predominant diastolic dysfunction.
Diastolic dyspnea (Dyspnea due to predominant diastolic dysfunction / HFPEF)
- Delayed dyspnea . It manifest well after the exertion is completed.
- It is more off a struggle to handle the venous return .The forward flow (Arterial circuit ) is relatively well toned and tuned and hence fatigue is rare .
- Typically it has a prolonged recovery time .(? > 1-2 minutes )
- Is it less harmful in terms of longevity ? May be . . . since it is more related to physical de-conditioning. Most of the physiological episodes of dyspnea are probably diastolic dysfunction mediated .
- Dyspnea that is triggered in diastole is also dependent very much on the heart rate .If the heart rate fail to reach the baseline the recovery of dyspnea is also delayed
- Some believe , physiological dyspnea should disappear within 30-60 seconds after termination of activity .(Highly arbitrary!)
The pressure volume loop in various forms of heart disease will determine the degree of myocardial stretch and the resultant dyspnea .Image source : http://www.1cro.com/medicalphysiology/chapter10/chap_10.htm
Systolic dyspnea (Dyspnea due to predominant systolic dysfunction )
- Patients with primary systolic pump failure experience dyspnea very early into exercise .
- Much of dyspnea occur during activity itself .
- Exercising muscles show hypoxia and hence fatigue is conspicuous .
- Recovery of dyspnea is relatively immediate as the activity is stopped .Demand from exercising muscle is significantly dropped.
- If the venous return is well handled by the ventricles the recovery phase is more comfortable .
Summary
In primary diastolic dysfunction ,the maximum stress to ventricle occurs when the venous return peaks that usually happen in the exercising muscles , as they shed vaso-dilatory property in post exertion phase .
Management Implication
Fluid overload , Tachycardia are more related to diastolic dysfunction .(Beta blockers by prolonging the diastole can , provide important relief of dyspnea in diastolic dysfunction (In HOCM patients this action could be more important that the much hyped negative inotropism !)
Final message
Dyspnea is a complex cortical perception , influenced by filling pressure of heart, stretch receptor in lungs , respiratory and exercise muscle . It is further impacted by number of biochemical parameters (Lactate/ O2 etc )
Of-course , it could be a far fetched imagination to split dyspnea mechanism with reference to cardiac cycle. Combinations of both systolic and diastolic dysfunction is the norm in many cardiac conditions . However , I believe we need more insight in the pathogenesis of this , “most important symptom” that emanate from the heart .
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Dr.S.Venkatesan MD 