In-shoe pressure measurements with a viscoelastic heel orthosis.

OBJECTIVE: To detect the mechanical effect of a viscoelastic heel orthosis. DESIGN: Two-factor analysis of variance with interactions between the orthosis and the subjects. The number of subjects was determined by presuming the effect of the orthosis to be twice as large as the error-free standard deviation (SD) of the interactions, the step-to-step SD four times as large as the error-free SD of the interactions, type 1 error probability equal to .05, and type 2 error probability equal to .20. SETTING: A gait laboratory in a university hospital. SUBJECTS: Twenty-two consecutive patients with treated heel pain. MAIN OUTCOME MEASURES: Peak pressure (PP), pressure-time integral (PTI), and foot-to-sensor contact time (CoT) measured for five steps at 24 discrete sensors of predetermined positions in the foot with treated heel pain. RESULTS: The orthosis reduced PPs, PTIs, and CoT (p < .05) in the median midfoot and lateral midfoot; reduced PPs and PTIs (p < .05) in the posterior heel and medial midfoot; increased PP and PTI (p < .05) in the anterior part of the first metatarsal head; and increased PTI (p < .05) in the lateral part of the hallux. The ratios of the estimated step-to-step SDs to the estimated error-free SDs of the interactions of PPs, PTIs, and CoT were less than four at all the sensors. CONCLUSION: Proper design and estimation of the variations ensured that there was sufficient power to detect the effect of an a priori specified size as statistically significant: the orthosis reduced the mechanical loads in the posterior heel and the midfoot and increased the mechanical loads in the anterior part of the first metatarsal head and the lateral part of the hallux during walking.

Normal standards for cardiopulmonary responses to exercise using a cycle ergometer test.

The purpose of the study was to establish standards for cardiopulmonary responses to exercise in healthy Chinese subjects in Taiwan. One hundred and five sedentary healthy subjects, 55 men and 50 women aged between 20 and 75 years, were tested. They pedalled a cycle ergometer with the work rate increased by 10 W every minute until they were exhausted. Expiratory gas volume, oxygen concentration, carbon dioxide concentration, and heart rate were measured during the exercise test. Work rate (WRmax), oxygen consumption (VO2max), oxygen consumption divided by body weight (VO2max/BW), heart rate (HRmax), and ventilation (VEmax) at maximal exercise, and oxygen consumption at anaerobic threshold (VO2AT) were determined. These parameters were regressed by age (A, in year), height (H, in cm), body weight (G, in kg), and gender (S, 0 = women, and 1 = men), and the following predictive equations were obtained: 1) WRmax (W) = -1.2 A + 1.1 H + 0.7 G + 28 S - 56, R = 0.90; 2) VO2max (ml/min) = -20 A + 9.5 H + 16 G + 461 S - 237, R = 0.90; (3) VO2max/BW (ml/kg/min) = -0.31 A + 0.14 H - 0.14 G - 7.2 S + 22, R = 0.87; 4) HRmax (beat/min) = -0.81 A + 209, R = 0.61; 5) VEmax (L/min) = -0.74 A - 0.04 H + 0.93 G + 22.2 S + 42, R = 0.83; 6) VO2AT (ml/min) = -9.5 A + 3.5 H + 9.4 G + 140 S - 122, R = 0.79. Our results provide normal standards for cardiopulmonary responses to exercise during cycle ergometer testing in Taiwan.

Submaximal oxygen pulse divided by body weight during incremental exercise test.

The purpose of this study was to examine whether submaximal oxygen pulse divided by body weight (O2 pulse/BW) during an incremental exercise test discriminated between trained and untrained men, correlated to left ventricular ejection fraction (LVEF) at rest in post-myocardial infarction patients, and was sensitive and specific in detecting ventricular dysfunction and mild ventricular dysfunction with myocardial ischemia during exercise. Forty-three trained men, 44 untrained men, and 21 post-myocardial infarction patients pedaled a cycle ergometer, with O2 consumption, heart rate, and myocardial ischemia monitored during the exercise test. Work rate started at 10 W and increased 10 W/min stepwise; the O2 pulse and O2 pulse/BW at 10 through 120 W were calculated. The LVEF of the patients was measured at rest using radionuclide ventriculography three weeks after myocardial infarction. The results revealed that O2 pulse/BW was significantly different between trained and untrained men at 80, 90, 100, 110, and 120 W, whereas O2 pulse was significantly different only at 110 and 120 W. Oxygen pulse/BW at 10 W, as well as 30 through 120 W, significantly correlated to LVEF in the patients. The three patients with ventricular dysfunction (LVEF, < 40%) plus the two patients with mild ventricular dysfunction (LVEF between 40 and 50%) and ST segment depression during exercise all had submaximal O2 pulse/BW significantly lower than untrained men (sensitivity, 100%). Among the 11 patients with normal ventricular function (LVEF, > 50%) plus the 5 patients with mild ventricular dysfunction but no ST segment depression, 13 patients did not have submaximal O2 pulse/BW significantly lower than untrained men (specificity, 81%).

The mechanism of plantar unloading in total contact casts: implications for design and clinical use.

Although the total contact cast (TCC) has been shown to be an extremely effective treatment for the healing of plantar ulcers in diabetic patients, little is known about the biomechanics of its action. In this study, plantar pressure and ground reaction force measurements were obtained from over 750 foot contacts as five subjects with known elevated plantar forefoot pressures walked barefoot, in a padded cast shoe, and a TCC. Peak plantar pressures in the forefoot were markedly reduced in the cast compared with both barefoot and shoe walking (reductions of 75% and 86% respectively, P < 0.05). Peak plantar pressures in the heel were not, however, significantly different between the shoe and the TCC, and the longer duration of heel loading resulted in an impulse that was more than twice as great in the cast compared with the shoe (P < 0.05). An analysis of load distribution indicated that the mechanisms by which the TCC achieves forefoot unloading are (1) transfer of approximately 30% of the load from the leg directly to the cast wall, (2) greater proportionate load sharing by the heel, and (3) removal of a load-bearing surface from the metatarsal heads because of the "cavity" created by the soft foam covering the forefoot. These results point out some of the "essential design features" of the TCC (which are different from what had been previously supposed), support the use of the TCC for healing plantar ulcers in the forefoot, but raise questions about its utility in the healing of plantar ulcers on the heel.

Exercise test in acute myocardial infarction.

Although maximal oxygen consumption (VO2max) and oxygen consumption at anaerobic threshold (VO2AT) were used to measure cardiac function, the clinical significance in acute myocardial infarction (MI) has not been reported. The purpose of this study was to compare VO2max and VO2AT between post-MI patients and healthy men and to correlate the parameters to other clinical measures. Forty-three active healthy men, 44 sedentary healthy men, and 43 post-MI patients were studied using incremental cycle exercise test. Their work rates, oxygen consumption, heart rates, oxygen pulses, ventilation, and other parameters at VO2max and VO2AT were determined with spirometer, gas concentration analyzer, and electrocardiograph. Anaerobic threshold was determined by analyzing the ventilatory parameters. Most of the exercise test parameters at VO2max were greatest in the active men, intermediate in the sedentary men, and least in the post-MI patients (P < 0.01) whereas the rate-pressure products of the active men and sedentary men were not significantly different from each other and were greater than those of the post-MI patients (P < 0.01). In the post-MI patients, VO2max was inversely correlated to the peak serum level of creatine phosphokinase MB isoenzyme (P < 0.01) and associated with extensive infarction (P < 0.05). Most of the parameters at VO2AT were greater in the active men than in the sedentary men (P < 0.01) but not significantly different between the sedentary men and post-MI patients. In the post-MI patients, VO2AT was significantly correlated to left ventricular ejection fraction (P < 0.01) and associated with heart failure (P < 0.05). The results revealed that VO2max and VO2AT had different clinical significance in post-MI patients; VO2max was related to the infarct size, and VO2AT was related to the pumping function of heart.