Biomedical subjects

C R Wyss

Publications and source records attributed to C R Wyss.

At least 19 recordsLinked to original sources

PubMed1995

A model for the study of wounds in normal elderly adults and patients with peripheral vascular disease or diabetes mellitus.

The purpose of the study was to test the hypothesis that significant delays in cutaneous wound healing could be demonstrated using standard wounds and high quality histological methods in patients with severe peripheral vascular disease (PVD) and/or diabetes mellitus (DM) compared to healthy elderly controls. Additionally, we proposed that standard wounds on the arms of elderly controls would heal more rapidly than comparable wounds on the legs. In order to test these hypotheses we developed and characterized a partial thickness wound model which could be used safely in human subjects. The study population consisted of 25 elderly normal volunteers, 17 patients with PVD, and 24 patients with DM. Standard wounds were created using a Simplate II bleeding-time device. A total of 309 wounds ranging in age from 1 to 25 days were determined to be suitable for analysis. A global index of wound maturity was developed based on selected epidermal and dermal events of repair which could be scored histologically. The superficial component (within 0.1 mm of the epidermis) and deep components of dermal wounds were analyzed separately. Simultaneously created arm and leg wounds were studied in 15 of the elderly controls. Transcutaneous partial pressure of oxygen (TcPO2) measurements were used to estimate the severity of cutaneous ischemia. Data analysis revealed that the most striking differences observed were in dermal events of repair. Control wounds were more mature than dermal wounds from patients with PVD (P < 0.05). A significant reduction in the number of neutrophils and macrophages (P < 0.05) was demonstrated in 7-day-old wounds of patients with PVD compared to controls. Patients with DM showed a similar trend of reduced wound maturity but it did not reach statistical significance. Wounds created in skin with TcPO2 > 20 were more mature than wounds with TcPO2 < or = 20 (P < 0.05) and arm wounds were more mature than leg wounds (P < 0.01). The most significant difference noted in this wound model was that the superficial compartment of dermal wounds was significantly more mature than the deep compartment (P < 0.001). Good agreement was observed between two independent scorers of wound histology and no complications were noted in either patients or controls when using this human wound model. We conclude that the model described allows evaluation of both epidermal and dermal events of repair with relative safety even in patients with PVD and DM.(ABSTRACT TRUNCATED AT 400 WORDS)

Aged↗

PubMed1990

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 (greater than 40 mm Hg) and low (less than 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Circulatory and mechanical response of skin to loading.

We investigated the tolerance of skin to mechanical loading over the tibia and over the tibialis anterior muscle in 12 normal volunteers. Surface load, subcutaneous tissue pressure, skin deformation under load, and transcutaneous partial pressure of oxygen (TcPO2) were simultaneously monitored. The skin over bone showed a significantly stiffer load deformation relationship than the skin over muscle (p less than 0.001). The displacement required to reduce TcPO2 to 0 over bone, 1.1 +/- 0.3 mm (mean +/- standard deviation), was significantly less than that required over tibialis anterior muscle, 5.4 +/- 1.1 mm (p less than 0.001). The applied pressure required to reduce TcPO2 to 0 was significantly greater for skin over muscle (71 +/- 16 mm Hg) than for skin over bone (42 +/- 8 mm Hg) (p less than 0.001). However, the subcutaneous pressure required to reduce TcPO2 to 0 was not significantly different for skin over muscle (36 +/- 11 mm Hg) than for skin over bone (28 +/- 10 mm Hg) (p greater than 0.05). Our results indicate that skin over muscle tolerates greater locally applied loads and deformations because the pressure is lower within the tissue than when similar loads and deformation are applied to skin over bone. Cutaneous perfusion, as indicated by TcPO2, seems to be linked more closely to the subcutaneous tissue pressure than to the surface load or deformations. These results provide some data for predicting mechanical and physiologic response to locally applied loads such as those that may be encountered in prosthetic wear.

Adult↗

PubMed1988

Transcutaneous oxygen tension as a predictor of success after an amputation.

We measured local transcutaneous oxygen tension at the foot and proximal and distal to the knee in 162 patients who then had 206 amputations. When the values for oxygen tension at the foot and distal to the knee were compared with the success or failure of healing after an amputation of the foot or distal to the knee, respectively, a clearly increasing probability of failure was correlated with decreasing transcutaneous oxygen tension. However, even at a tension of zero the probability of failure was not 100 per cent. The results were similar for diabetic and non-diabetic patients. Preoperative values for transcutaneous oxygen tension were a much more consistent predictor of success or failure of healing after an amputation of the foot or distal to the knee than were measurements of systolic blood pressure at the ankle, but neither was predictive of the outcome after an above-the-knee amputation.

Amputation, Surgical↗

PubMed1987

Reliability of transcutaneous oxygen tension (TcPO2) measurements in elderly normal subjects.

This study was conducted to evaluate the reliability of TcPO2 measurements in a well characterized group of 10 elderly normal subjects with an age distribution typical for the population with peripheral vascular disease (PVD) and amputation. The TcPO2 values were obtained on three separate occasions at 2-week intervals at seven anatomic sites commonly measured in patients with PVD. The TcPO2 values were comparable to those previously reported for similar sites in normal elderly subjects. Measurement to measurement variation averaged 1.1 kPa (8 mmHg) for a coefficient of variation (CV) of 14.4%. Confidence intervals ranging from 2.1 kPa (16 mmHg) above a single TcPO2 value to 2.1 kPa (16 mmHg) below were necessary to contain the true value 95% of the time. While TcPO2 measurement is assuming an important role in the evaluation of disease states in both paediatric and adult medicine, our observations emphasize the importance of using such measurements as an adjunct in clinical decision making and not basing such decisions on a single TcPO2 value alone. The size of the confidence intervals can be reduced substantially for a given site by taking the mean of two or more TcPO2 measurements taken at separate times.

Aged↗

PubMed1987

Does inadequate oxygen delivery trigger pressor response to muscle hypoperfusion during exercise?

In dogs running on a treadmill at 2 or 4 mph or 4 mph plus 10% incline, graded reductions in hindlimb perfusion reflexly elicited pressor responses. To test the idea that systemic arterial pressure (SAP) is raised by accumulation in muscle of a nerve-activating "pressor substance" release when O2 delivery becomes inadequate, arterial O2 content (CaO2) was reduced 29.1% by carbon monoxide (CO) inhalation before repeating exercise at 2 mph. We reasoned that the pressor substance, or related substances, should appear in femoral venous blood and be correlated to SAP. [K+] behaved inappropriately as a signal to raise SAP, i.e., when flow was reduced, SAP rose markedly with little or no change in [K+]. SAP was well correlated to pH and [lactate] over the three work loads. Compared with the same work load with normal CaO2, CO shifted the relation between SAP and terminal aortic flow rightward 0.30 l/min (34.5%) and the relation between SAP and PO2 leftward 7.7 mmHg. CO did not affect the relation of SAP to terminal aortic O2 delivery, hindlimb O2 uptake index, pH, or [lactate]. Thus pressor responses are apparently generated when O2 delivery falls below some critical level causing accumulation of a pressor substance the release of which is linked to a metabolic event that precipitates lactate accumulation.

Animals↗

PubMed1987

Total shoulder arthroplasty.

A prospective study was done of fifty total shoulder replacements in forty-four patients who were followed for an average of 3.5 years (range, 2.0 to 7.5 years). The preoperative diagnosis was osteoarthritis in thirty-three shoulders, rheumatoid arthritis in eleven, and a previous fracture of the humeral head in six shoulders. Nine of the shoulders had a tear of the rotator cuff. The Neer-II system of total shoulder replacement with a non-metal-backed component was used in all fifty shoulders. At follow-up, forty-four shoulders (88 per cent) had no significant pain. Of the six painful shoulders, four had loosening of the glenoid component and one had malposition of both components. Three of the six shoulders had no significant pain after revision. The average range of active forward elevation in all of the shoulders improved from 71 to 100 degrees, and both external and internal rotation improved as well. Five specific activities of daily living were evaluated, and the patients' ability to perform them improved from 14 to 78 per cent. Thirty-five shoulders (68 per cent) were rated by the patients as much better; thirteen shoulders (26 per cent), as better; and three (6 per cent), as no better. An incomplete lucent line was noted around five (10 per cent) of the cemented humeral stems and around thirty-seven (74 per cent) of the glenoid prostheses. Four arthroplasties (8 per cent) required revision: three for loosening of the glenoid component and one for malposition of both components.(ABSTRACT TRUNCATED AT 250 WORDS)

Activities of Daily Living↗

PubMed1987

Relationship between transcutaneous oxygen tension, ankle blood pressure, and clinical outcome of vascular surgery in diabetic and nondiabetic patients.

We measured ankle systolic blood pressure (ABP) and limb transcutaneous oxygen tension (TcPO2) before and after 53 vascular procedures performed to relieve limb-threatening ischemia. We compared changes in ABP and TcPO2 and also compared these measurements of limb hemodynamics with the clinical outcome of the vascular procedures. For the procedures performed on patients without diabetes, both ABP and TcPO2 registered similar changes after surgery. Furthermore, those nondiabetic patients who had a postoperative ABP greater than 75 mm Hg or TcPO2 greater than 20 mm Hg showed resolution of the clinical symptoms within 60 days after surgery. All patients falling below these levels underwent a subsequent limb amputation. The results differed somewhat for procedures performed on patients with diabetes. First, a number of diabetic patients showed high ABP in conjunction with low TcPO2. We attribute these observations to the high incidence in diabetic patients of calcific medial stenosis leading to artificially elevated ABP measurements. Second, the clinical outcome among diabetic patients was uncorrelated with the postoperative ABP and was poorly correlated with postoperative TcPO2. Those diabetic patients with postoperative TcPO2 below 20 mm Hg showed unfavorable clinical outcomes, but many patients with postoperative TcPO2 greater than 20 mm Hg and postoperative ABP greater than 75 mm Hg also showed unfavorable clinical outcome (slow healing of ulcers, persistence of rest pain, and/or an amputation on the limb). These data suggest that among our patients with diabetes, simple relief of limb ischemia was not sufficient to result in a trouble-free clinical course. We conclude that TcPO2 is a useful replacement or adjunct to ABP measurements for evaluating the hemodynamic outcome of vascular surgery. Our results also suggest that it is extremely important to evaluate the outcome of such surgeries separately in patients with and without diabetes.

Adult↗

PubMed1986

Factors relating to the sensory acuity of limbs with peripheral vascular insufficiency.

We examined several possible causes for the high incidence of poor sensory acuity in the limbs of 176 patients with moderate to severe peripheral vascular insufficiency. We investigated the relationships of diabetes, alcoholism, and smoking, as well as the severity of peripheral vascular disease, to the integrity of basic sensory modalities such as two-point discrimination and perception of light touch. The presence or absence of diabetes exerted the strongest effect on peripheral sensation. In patients who did not have diabetes, sensation in the limbs was most strongly affected by whether the patient was an alcoholic. Smoking did not have a significant effect on limb sensation. Among nondiabetic, nonalcoholic patients, there was a weak residual effect related to the severity of the peripheral vascular insufficiency. Even among these patients, however, systemic factors predominated in determining the loss of sensation. We also examined the extent to which loss of sensation might be related to the development of ulcers. Among patients who were not diabetic, there was a highly significant relationship between loss of sensation and the presence of limb ulceration. Surprisingly, however, there was no discernable relationship between the presence of ulcers in diabetic patients and the degree of loss of peripheral sensation. This result suggests that a large percentage of ulcers seen in diabetic patients are not of neurogenic origin.

Adult↗

PubMed1986

The nature of the exercise stimulus.

The two foremost hypotheses concerning the nature of the exercise stimulus are: Central Command. Centrally generated signals activate in parallel cardiovascular and skeletal muscle motor systems; Muscle Chemoreflex. Chemosensitive nerves within the skeletal muscle detect local accumulations of metabolites which reflect disparities between muscle blood flow and metabolism. The focus is mainly on the second hypothesis. The neurophysiological basis for this reflex is well established. Accumulations of metabolites within ischemic muscle reflexly trigger pressor responses that are abolished by blockade of sensory nerves from muscle. However, such blockade does not abolish circulatory responses to static or mild dynamic exercise. To assess the importance of muscle chemoreflexes, stepwise partial occlusions of the terminal aorta were made in exercising dogs. The rise in arterial pressure was related to reductions in terminal aortic flow and arterial pressure below the occluder. In mild exercise sensitivity of the reflex was low until flow was substantially reduced to a threshold. In heavier exercise sensitivity of the reflex was high (no threshold) and could provide a tonically active exercise stimulus. The nature of the metabolic signal is unknown. The pressor response was most closely related to femoral venous lactate concentration and unrelated to femoral venous K+ or PO2.

Animals↗

PubMed1984

Long-term responses of atrial rate and peripheral resistance to changes in ventricular pacing rate in awake dogs with atrioventricular block.

We wished to see if a maintained change in pressure at the baroreceptors leads to a maintained or a transient change in heart rate and total peripheral resistance, and if long-term changes in rate and resistance paralleled one another. In awake dogs with intact baroreceptors and complete atrioventricular block, ventricular rate was held alternately at high (90 beats/min) and low (50 beats/min) levels, each for 2 days. This cycle was repeated several times. Data were recorded for 1.5 hours each day. With this change in ventricular rate, there was a maintained change over 2 days in arterial (14.4 +/- 1.0 mm Hg) and central venous (3.0 +/- 1.2 mm Hg) pressures. These changes in pressure were accompanied by a maintained change in atrial rate of 41.1 +/- 9.4 beats/min; peripheral resistance, however, changed only transiently. In three animals, the half-cycle length was 1 week. Changes in heart rate also persisted for this period. It appears from these studies that there is long-term control of heart rate, but not of peripheral resistance. Hypotheses to explain these results are presented.

Animals↗

PubMed1984

Changes in vascular capacity in awake dogs in response to carotid sinus occlusion and administration of catecholamines.

Changes in cardiac filling pressure (central venous pressure) were measured following carotid occlusion and infusions of catecholamines in awake dogs while cardiac output was held constant. After carotid occlusion in dogs with vagi blocked, central venous pressure increased about 0.8 mm Hg (an estimated decrease in vascular capacity of 2.4 ml/kg). Carotid occlusion before vagal block or following vagal block and beta-adrenergic block with propranolol caused no significant changes in central venous pressure. Phenylephrine (0.1-2.0 micrograms/min per kg) caused dose-dependent increases in arterial pressure, but changed central venous pressure (ca. 2.5 mm Hg) only at the highest doses. Epinephrine in doses (0.03-0.51 micrograms/min per kg) that caused little change in arterial pressure increased central venous pressure up to 5.3 mm Hg (an estimated decrease in vascular capacity of 12.0 ml/kg); this response was attenuated about 50% by propranolol. Isoproterenol (0.01-0.40 micrograms/min per kg) decreased arterial pressure and caused changes in central venous pressure similar to those seen with epinephrine. These responses were abolished by propranolol. Vascular compliance, determined from the change in central venous pressure following known changes in vascular blood volume, averaged 3.0 +/- 0.6 ml/mm Hg per kg. In the conscious, resting dog, both alpha- and beta-adrenergic receptors are involved in the reflex control of cardiac filling pressure. The beta-adrenergic responses predominate.

Animals↗

PubMed1984

The relationship of transcutaneous PO2 and laser Doppler measurements in a human model of local arterial insufficiency.

Transcutaneous PO2 and laser Doppler measurements were made over areas of unheated and heated skin of the feet of normal volunteers. Stepwise elevation of the foot above the level of the heart systematically reduced the local arterial pressure and, thus, the local arteriovenous gradient in these areas. Results indicated that transcutaneous PO2 and laser Doppler measurements reflect changes in local arteriovenous gradient when made over areas of warmed skin, but not unwarmed skin. Comparison of skin surface and subcutaneous temperatures obtained with two heater types revealed the importance of heater configuration. Results confirm a previously hypothesized nonlinear relationship between transcutaneous PO2 and local cutaneous blood flow and indicate that a transcutaneous PO2 reading of zero may be obtained in the presence of significant local cutaneous blood flow.

Arterial Occlusive Diseases↗

PubMed1984

Transcutaneous oxygen tension measurements on limbs of diabetic and nondiabetic patients with peripheral vascular disease.

We measured transcutaneous oxygen tension (TcPo2) at a skin temperature of 44 degrees C on 319 limbs in an approximately equal number of nondiabetic and diabetic patients with peripheral vascular disease. Measurements were made above the knee, below the knee (BK), and on the dorsum of the foot. Nondiabetic limbs with leg/foot (the lesser of BK or foot) TcPo2 values below 20 mm Hg were significantly more likely to have ulcers, to have rest pain, or to require an amputation on the limb as compared with limbs with leg/foot TcPo2 values above 20 mm Hg. Patients with more severe symptoms had significantly reduced limb TcPo2 values, and these values were lower at more distal measurement sites. Generally, these results were similar in diabetic and nondiabetic patients without limb ulceration; however, the diabetic patients were more likely to have ulcers in the presence of high limb TcPo2. This observation suggests that ulceration in a substantial proportion of the diabetic patients may have resulted from factors other than insufficient cutaneous tissue oxygen delivery.

Aged↗

PubMed1984

The effect of exercise upon cutaneous oxygen delivery in the extremities of patients with claudication and in a human laboratory model of claudication.

Transcutaneous PO2 measurements have been shown previously to reflect local cutaneous oxygen delivery in patients with severe peripheral arterial insufficiency. In the present studies, transcutaneous PO2 measurements indicated that exercise of the involved extremity lowered cutaneous oxygen delivery in patients with moderate peripheral arterial insufficiency (claudication). These exercise-related changes in transcutaneous PO2 were reproduced in a human laboratory model of claudication. The pattern of change in transcutaneous PO2 observed in this model during and after exercise correlated closely with the pattern of change in mean systemic blood pressure during the same time period.

Ankle↗

PubMed1983

Cardiovascular responses to graded reductions in hindlimb perfusion in exercising dogs.

In six dogs trained to run at 2, 4, and 6 mph, we caused graded reductions in hindlimb perfusion by compressing the terminal aorta. Our goal was to examine the relationship between hindlimb perfusion [terminal aortic flow (TAQ) and femoral arterial pressure (FP)] and cardiovascular responses [aortic pressure (AP), heart rate, and ascending aortic flow (CO)]. Small reductions in TAQ and FP produced bradycardia, small decreases in CO, and small increases in AP. Further reductions in TAQ and FP produced tachycardia, increased CO, and large increases in AP. AP rose by about 1 mmHg for each 1-mmHg fall in FP. The response was similar at all speeds, but as work load increased it required smaller reductions in FP and TAQ to cause a pressor response (e.g., at 6 mph we could not demonstrate a nonlinear relationship between TAQ and AP). At low work loads the cardiovascular responses to exercise were most likely set by signals other than feedback from exercising muscle because substantial reductions in hindlimb perfusion caused no significant cardiovascular responses. At moderate-to-high work loads or where muscle perfusion is restricted, metabolic feedback from muscle may play a role in cardiovascular responses to exercise.

Animals↗

PubMed1982

Beat-by-beat control of cardiac output in awake dogs with atrioventricular block.

In dogs with atrioventricular block and implanted ascending aortic flow probes, cardiac output can be controlled on each beta. The procedure is implemented through on-line use of a digital computer. The algorithm has three steps: 1) aortic flow is measured and integrated to give stroke volume; 2) at the end of ejection, the program computes how long the current beat must be to keep cardiac output at a target level; and 3) the ventricle is stimulated at the proper time. Cardiac output can be controlled over a range of 60-110% of normal in a resting dog. This range can be expanded by combining hemorrhage or volume infusion with the control procedure.

Animals↗

PubMed1982

The effects of compression and elevation on the circulation to the skin of the hand as reflected by transcutaneous PO2.

Transcutaneous PO2 has been used in a group of four normal subjects to noninvasively indicate the effects of compression and limb elevation on the circulation to the skin of the hand. Both compression and elevation of the hand reduced the local transcutaneous PO2. A combination of compression and elevation had a significantly greater effect than either of these modalities applied singly. The observations in this study suggest that the effect of hand elevation compression are mediated through a reduction in the local arteriovenous gradient. Although hand elevation and compression are clinically useful in the control of hand swelling, the hand surgeon should be aware of their potential deleterious effects on local circulation, particularly when they are used in combination.

Adult↗