D. B. Friedman

Left ventricular pressure-volume and Frank-Starling relations in endurance athletes. Implications for orthostatic tolerance and exercise performance.

BackgroundEndurance athletes have a high incidence of orthostatic intolerance. We hypothesized that this is related to an abnormally large decrease in left ventricular enddiastolic volume (LVEDV) and stroke volume (SV) for any given decrease in filling pressure. Methods and ResultsWe measured pulmonary capillary wedge (PCW) pressure (Swan-Ganz catheter), LVEDV (two-dimensional echocardiography), and cardiac output (C2H2 rebreathing) during lower body negative pressure (LBNP, −15 and −30 mm Hg) and rapid saline infusion (15 and 30 ml/kg) in seven athletes and six controls (V˙o2max, 68 ± 7 and 41 ± 4 ml/kg/min). Orthostatic tolerance was determined by progressive LBNP to presyncope. Athletes had steeper slopes of their SV/PCW pressure curves than nonathletes (5.5 + 2.7 versus 2.7 + 1.5 mI/mm Hg, p < 0.05). The slope of the steep, linear portion of this curve correlated significantly with the duration of LBNP tolerance (r = 0.58, p = 0.04). The athletes also had reduced chamber stiffness (increased chamber compliance) expressed as the slope (k) of the dP/dV versus P relation (chamber stiffness, k = 0.008 ± 0.004 versus 0.031 ± 0.004, p < 0.005; chamber compliance, l/k = 449.8 + 283.8 versus 35.3 ± 4.3). This resulted in larger absolute and relative changes in end-diastolic volume over an equivalent range of filling pressures. ConclusionsEndurance athletes have greater ventricular diastolic chamber compliance and distensibility than nonathletes and thus operate on the steep portion of their Starling curve. This may be a mechanical, nonautonomic cause of orthostatic intolerance.

Cardiovascular responses to active and passive cycling movements

Ten healthy subjects were evaluated at rest and at 5 min of unloaded active (AC) and passive (PC) cycling. Passive limb movements were accomplished using a tandem bicycle with a second rider performing the movements. We measured heart rate (HR), mean arterial pressure (MAP), cardiac output (CO), oxygen uptake (VO2), rating of perceived exertion (RPE), and electrical activity (EMG) of lower limbs muscles. Values for stroke volume (SV) and peripheral vascular resistance (PVR) were calculated. EMG, RPE, and VO2 were higher during AC than during PC (P < 0.001). CO increased during both modes of cycling, but during AC it resulted from a HR acceleration (73 +/- 2 at rest to 82 +/- 2 beats.min-1 at 60 rpm; P < 0.001) with no change in SV whereas during PC, SV increased from rest (65 +/- 4 at rest to 71 +/- 3 ml at 60 rpm; P = 0.003) along with no change in HR. PVR remained constant during PC, but decreased by 13% during AC (P < 0.001) and MAP increased only during PC (93 +/- 2 at rest to 107 +/- 2 mm Hg at 60 rpm). These results supports the concept that central command determines the HR response to dynamic exercise. The increase in SV and consequently in MAP during PC was probably due to increased venous return and/or to muscle mechanoreceptor-evoked increased myocardial contractility.

Compliance and efficacy of cardiac rehabilitation and risk factor modification in the medically indigent

To compare the compliance and efficacy of cardiac rehabilitation in medically indigent patients with more affluent patients, we evaluated the first 65 patients referred to a new cardiac rehabilitation program of whom 36 were medically indigent (i.e., dependent on Medicaid for health care reimbursement) and 29 were funded by private medical insurance. Attendance during 12 weeks of monitored, supervised, phase II cardiac rehabilitation was examined retrospectively. In addition, training history, cardiovascular response to submaximal exercise, dietary fat intake, and smoking incidence were studied at baseline and repeated prospectively between 6 months and 1 year (8.2 +/- 1.1 months) after program completion. Both the indigent and private patients attended >90% of scheduled sessions and achieved a significant improvement in submaximal work capacity which was well maintained at the time of follow-up. Also, both groups continued to eat a diet low in saturated and total fat. The indigent patients smoked more before the program but were equally successful at quitting cigarette smoking as the private patients. We conclude that in the appropriate setting, indigent patients can successfully complete and maintain excellent compliance with a program of coronary risk factor modification including exercise training, dietary modification, and cessation of cigarette smoking, to a degree equivalent to more affluent and educated patients. Compliance may be enhanced by employing a small program emphasizing extensive personal contact with rehabilitation staff.

Heart rate and blood pressure responses at the onset of dynamic exercise: effect of Valsalva manoeuvre

AbstractThe influence of respiration on the mean blood pressure

Cardiovascular responses during static exercise. Studies in patients with complete heart block and dual chamber pacemakers.

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Regional distribution of blood flow of dogs during graded dynamic exercise

and R-R interval responses at the onset of dynamic exercise was studied in 15 healthy subjects who performed 4 s of unloaded cycling at 1.5–2.0 Hz, 4 s of Valsalva manoeuvre at 5.3 kPa, and a combination of both, each during a 12-s long apnoea at total lung capacity. The R-R intervals were obtained from the electrocardiogram,Pa was measured continuously by finger plethysmography, and intra-oral pressure was used to estimate the changes in intrapleural pressure. There was an immediate and significant shortening of the R-R intervals during exercise [mean (SE): 790 (20) to 642 (20) ms] that was not modified when Valsalva manoeuvre was added [783 (28) to 654 (21) ms]. Although 4 s of exercise alone did not alterPa [13.8 (0.5) to 13.7 (0.7) kPa], this may indicate a pressor response, since

Exercise-induced functional desensitization of canine cardiac beta-adrenergic receptors.

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