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Biomedical subjects

K C Welham

Publications and source records attributed to K C Welham.

7 recordsLinked to original sources
PubMed1984

Cardiac performance and myocardial blood flow in pigs with compensated right ventricular hypertrophy.

Compensated right ventricular hypertrophy (RVH), defined by a greater than 100% RV weight increase compared to 17 normal animals, was created in 17 young pigs by pulmonary arterial banding. RVH was associated with significant elevations (p less than 0.001) in RV peak dP/dt, RV stroke work, RV minute work and RV rate-pressure product compared to normal animals matched by body weight. RV peak dP/dt showed a positive correlation (p less than 0.001) with RV peak systolic pressure in normals; however, this relationship was lost in banded animals since progressively higher RV pressures were not associated with concomitant increases in RV peak dP/dt, thus, suggesting an intrinsic difference between right and left ventricles when working at systemic arterial pressures. Time to RV peak dP/dt became progressively longer (p less than 0.05) as RV weight increased in the RVH animals. When indices of cardiac work were normalized for RV weight, the RVH group could not be distinguished from normals suggesting that the performance per unit weight of RV muscle in RVH was unchanged. Total RV blood flow, measured by radioactive microspheres, closely followed (p less than 0.001) increases in RV mass in banded animals. Blood flow . g-1 muscle in RV and septal right side were unaltered in RVH; however, regional perfusion of the left ventricle (p less than 0.001) and septal right side were unaltered in RVH; however, regional perfusion of the left ventricle (p less than 0.001) and septal left side (p less than 0.02) increased significantly. There were regional variations in RV perfusion which were maintained in compensated RVH; stress (isoprenaline infusion) caused significant increases in blood flow to all regions of the heart in normal and RVH animals (p less than 0.001), but relative regional distribution was maintained. Our observations suggest a relationship between myocardial work and blood flow in RVH such that RV perfusion . g-1 is elevated to meet haemodynamic requirements once RV regional work . g-1 become greater than normal.

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PubMed1983

Hemodynamics, regional myocardial blood flow, and sarcoplasmic reticulum calcium uptake in right ventricular hypertrophy and failure.

Either right ventricular hypertrophy (RVH) or failure (RVF) was produced by pulmonary arterial banding in 47 piglets aged 3-6 weeks. When sufficient time was allowed to elapse after banding, RVH was present in 30 and had progressed to RVF in 17. These two groups were compared with 24 control, i.e., normal pigs (C). Animals with RVF differed from RVH and C animals by having reduced cardiac output and clinical signs of failure. Both RVH and RVF had significantly elevated right ventricular peak systolic pressures (RVS), weights (GMRV), and RV/LV systolic pressure ratios (these variables all increased greater than 100% compared with C). The RV (dP/dt)max correlated with RVS in C (r = 0.687, P less than 0.001), but this relationship was absent in RVH with higher RVS and GMRV. The RV (dP/dt)max correlated closely with RV blood flow/g per min in C (r = 0.638, P less than 0.01) and in RVH (r = 0.462, P less than 0.02). Calcium uptake by RV sarcoplasmic reticulum (SR) was diminished in RVH compared to C and further diminished in RVF (38%, P less than 0.001). Calcium uptake by LV SR also fell in RVF, suggesting that SR calcium uptake is merely a passive reflection of myocardial function. Our results also suggest that hemodynamic and subcellular changes seen in RVF may be detected during the compensated stage of RVH.

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PubMed1978

The first derivative of the transthoracic electrical impedance as an index of changes in myocardial contractility in the intact anaesthetised dog.

The suitability of the peak value of the first derivative of the thoracic electrical impedance dZ/dtmax has been investigated in dogs as a non-invasive index of changes in myocardial contracility by comparing if with the peak left ventricular dP/dt and the peak values of aortic blood velocity and acceleration. An increase in the inspired halothane concentration was used to produce changes in contracility. In 5 dogs the combined values for the correlation coefficient between dZ/dtmax peak velocity and acceleration were respectively 0.937, 0.954 and 0.950. In 14 out 15 comparisons p less than 0.001 and in one, p less than 0.01. On these grounds, dZ/dt max is proposed as a variable worthy of sconsideration in patient monitoring.

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PubMed1978

Experimental right ventricular hypertrophy and failure in swine.

Following pulmonary arterial constriction, 22 pigs developed right ventricular failure and 10 right ventricular hypertrophy. Comparing results with those obtained in 21 normal pigs (no pulmonary artery constriction), it was found the right ventricular peak systolic and end-diastolic pressures, cardiac output, and right ventricular weight distinguished hypertrophied and failing hearts from normal ones. Cardiac output was lower in failing hearts than in hypertrophied hearts and was the only variable which significantly differentiated between these two groups. Left ventricular pressures and left ventricular and right ventricular dP/dtmax, and maximum [(dP/dt)/P] did not distinguish failing from hypertrophied hearts. Left ventricular pressure, maximum [(dP/dt)/P] and left ventricular and right ventricular dP/dtmax were not significantly different in the three groups.

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PubMed1976

The effect of a progressive decrease in the circulating blood volume of the dog on the transthoracic impedance.

The correlations between the haemodynamic and transthoracic electrial impedance changes resulting from a progressive reduction in the circulating blood volume were studied in four intact mongrel dogs artificially ventilated with a mixture of halothane in nitrous oxide-oxygen. The cardiac output of the dogs was measured by both the electrical impedance and the fibre optic dye dilution techniques. It was found that significant correlations existed between the blood lloss and the arterial blood pressure, the maximum first derivative of the transthoracic impedance, the Heather Index, the transthoracic impedance, the maximum rate of change of aortic pressure and the cardiac stroke work. There was also a good correlation between the dye and impedance cardiac output values, the impedance value always being higher than the corresponding dye value. The correlation between the Heather Index and the PEP/LVET ratio and 1/PEP2 varied markedly from dog to dog.

Animals↗
PubMedDate not supplied

Cardiovascular effects of neuromuscular blockade during induced hypothermia.

Young lambs were used to study the effects of progressive cooling and rewarming on cardiovascular function during neuromuscular blockade induced by gallamine. Initially, it was shown that gallamine exerted no immediate, direct haemodynamic effect in normothermic or hypothermic lambs (cooled by 10 degrees C). By comparison with hypothermic controls, neuromuscular blockade was associated with increases in left ventricular (LV) max dP/dt (153%; P less than 0.02) as cooling progressed, and even greater increases (232%; P less than 0.001) during rewarming. It was concluded that these changes seem likely to represent enhanced myocardial contractility since preload did not closely follow LV max dP/dt (heart rate and mean aortic pressure fell gradually during cooling but values were restored in the rewarming phase). LV max dP/dt in lambs given gallamine only after cooling also showed a similar response during rewarming. Results of this study may have clinical relevance relating to the mechanical recovery of the hypothermic heart in patients receiving neuromuscular blockade during cardiac surgery, and they argue against using gallamine as such an agent.

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