Richard M. Harrington

Effects of aerobic training on exercise tolerance and echocardiographic dimensions in untrained postmenopausal women

The cardiovascular effects of physical training were evaluated in a controlled trial involving 32 healthy, untrained, postmenopausal women. The subjects were randomly assigned to an aerobic exercise training program or a control group. The exercise group participated in at least three 40-minute supervised sessions per week for 8 months. Twenty-five subjects completed the study: eight in the control group and 17 in the training group. The training group had a significant increase over the training period in maximal oxygen consumption (27.3 +/- 4.6 ml/kg/min vs 30.8 +/- 5.4 ml/kg/min, p less than 0.05) and maximal treadmill exercise duration (9.8 +/- 2.6 minutes vs 11.3 +/- 2.2 minutes; p less than 0.05). The control group had no significant change in maximal treadmill exercise duration (9.0 +/- 1.2 minutes vs 9.2 +/- 1.4 minutes) but had a slight increase in maximal oxygen consumption (23.7 +/- 3.4 ml/kg/min vs 24.4 +/- 4.1 ml/kg/min, p less than 0.05). The training group had significant increases in M-mode echocardiographic left ventricular end-diastolic dimension (4.6 +/- 0.6 cm vs 4.8 +/- 0.4 cm, p less than 0.05) and calculated left ventricular ejection fraction (0.66 +/- 0.14 vs 0.74 +/- 0.12, p less than 0.05). M-mode echocardiograms demonstrated no significant change in left ventricular dimensions or wall thickness in the control group. In this group of untrained postmenopausal women, a training effect was associated with enhanced resting left ventricular ejection fraction and increased resting left ventricular end-diastolic dimension.

A comparison of convergent and bi-plane X-ray photogrammetry systems used to detect total joint loosening

X-ray photogrammetry is an accurate method of measuring structural displacements within the musculoskeletal system. Total joint implant alignment, migration and loosening are important clinical parameters which can be measured by X-ray photogrammetry. The purpose of this paper is to compare two different X-ray photogrammetry systems which are being used to study total joint parameters. The Seattle system uses a convergent geometry and the Cleveland system a bi-plane geometry. The accuracy of the two systems was compared by individually measuring the relative motion produced in an articulated plastic model. The model was designed to simulate the relative motion which can take place between the bone and a loose implant. The displacements of the model components were determined physically and photogrammetrically, and the error in the measurements was calculated for several conditions. Both systems measured relative component motion in the model with a root mean square error of 0.1 mm or less. In clinical use stainless steel markers are implanted in human subjects, and both systems measure distances with a r.m.s. error of 0.2 mm or less. The ease of usage, efficiency and flexibility of the two systems based on actual clinical experience reveals strengths and weaknesses in each which should be recognized when selecting a particular system.

The effects of age and peripheral vascular disease on the circulatory and mechanical response of skin to loading.

The skin and subcutaneous soft tissues of amputation residual limbs are required to withstand externally applied loads of greater magnitude than similar tissues of the intact lower limb. Increased age and poor circulatory status may contribute to the increased risk of tissue injury seen in this population. This study evaluates the effects of age and circulatory status as risk factors for skin injury resulting from externally applied forces. Twelve young control (YC), six elderly control (OC) and 11 subjects with peripheral vascular disease (PVD) were studied. After base-line ankle arm index (AAI) measurements, TcPO2 electrodes were applied 10 cm below the knee over the medial surface of the tibia and the muscle belly of tibialis anterior. TcPO2 measurements and tissue displacements were obtained under the influence of incremented, normally oriented, external loads. The sensitivity of the tissues to applied loads was determined by calculating the load at which the TcPO2 reached zero. The stiffness of the tissues (displacement/load) was calculated under high (>40 mm Hg) and low (<20 mm Hg) loading conditions. No difference was noted in tissue sensitivity to applied loads between the OC and YC populations. The TcPO2 decreased to zero in the PVD population at significantly lower applied loads than both the OC and YC populations. The tissue stiffness of the PVD and the OC populations over bone was greater than the YC population, but no significant differences were noted between the PVD and the OC populations. In summary, increased age does not result in a greater tissue sensitivity to externally applied loads, in spite of the demonstrated increased tissue stiffness. That is, increased age alone does not appear to contribute to an increased risk of pressure injury to the skin. Arterial PVD however, may result in a greater sensitivity to externally applied loads, and therefore, greater risk of pressure injury.

The Measurement Of Total Joint Loosening By X-Ray Photogrammetry

Failure of total joint replacement due to loosening of the composents either between the implant and cement or between the cement and bone is emerging as a late complication with an incidence as high as 20 percent. Loosening may not only cause pain but progressive loss of support for the prosthesis with eventual structural failure. Early diagnosis is important so that revision may be carried when deterioration or pain occurs. No method is currently available which clearly establishes loosening at an early stage except surgical exploration. We have devised a method based on our in vivo photogrammetry studies of patellar tracking patterns using metallic markers placed in bone near both components of the total joint. Stereo x-rays taken with the joint loaded and unloaded are measured for relative motion between the implant and the metallic markers. Laboratory studies using prosthetic hip components mounted in plastic bone have revealed the ability of this method to detect pistoning movements as small as 80 microns. These findings were confirmed by physical measurements.

Single Image X-Ray Photogrammetry System Used To Detect Total Joint Loosening

Loosening is the number one complication of total joint replacements. A direct method of measuring small motions between the prosthetic implant and the surrounding bone would allow the surgeon to evaluate replacement surgery or activity restrictions. Single plane x-ray photogrammetry uses stainless steel markers in the bone and prosthetic implant and a control frame in order to accomplish this measurement. Testing of models representing a total hip replacement and total knee replacement has shown that displacements can be measured with a root mean square error of less than 0.2 mm.