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Biomedical subjects

J C Longhurst

Publications and source records attributed to J C Longhurst.

133 records · Page 8Linked to original sources
PubMed1980

Cardiovascular responses to static exercise in distance runners and weight lifters.

Sixty individuals including 17 competitive weight lifters (CWL), 12 competitive long-distance runners (LDR), 7 amateur (noncompetitive) weight lifters (AWL), 14 heavy controls (HC), and 10 light controls (LC) were studied at supine rest and during static exercise at 40% of maximal voluntary contraction. Blood pressures were similar in all groups at rest (R) and exercise (EX), but the heart rate (HR) and calculated double product (DP) of the LDR were lower at rest (HR: 53 +/- 2.9 beats/min, DP: 6,346 +/- 402) and at fatigue (HR: 78 +/- 5.4 beats/min. DP: 12,739 +/- 1,011) compared to the control group (R-HR: 69 +/- 2.2 beats/min, DP: 8,553 +/- 372; EX-HR: 97 +/- 3.5 beats/min, DP: 16,345 +/- 836). The LDR demonstrated higher end-diastolic volume index (EDVI) and higher end-systolic volume index (ESVI) at rest (EDVI: 84 +/- 3.7, ESVI: 31 +/- 2.7 ml/m2) and at the time of fatigue (EDVI: 90 +/- 5, ESVI: 37 +/- 2.7 ml/m2) compared to the LC group (R-EDVI: 61 +/- 4.4, ESVI: 22 +/- 2.2; EX-EDVI: 75 +/- 3.4, ESVI: 27 +/- 3.2 ml/m2). The CWL, AWL, and control groups had similar HR, DP, and cardiac volumes at rest and during exercise. These data suggest that competitive endurance (dynamic exercise) training alters the cardiovascular response to static exercise. On the other hand, weight lifting (static exercise) training does not alter the cardiovascular response to static exercise.

Adult↗
PubMed1979

Exercise-induced ST elevation in patients without myocardial infarction.

A review of 6040 consecutive exercise tests yielded 106 patients without previous myocardial infarction (MI) who had exercise-induced ST elevation (greater than or equal to 0.5 mm in a 15-lead ECG system). In 46, ST elevation was correlated with left ventriculography and coronary angiography. Coronary artery disease (CAD) (greater than or equal to 70% narrowing) was detected in 40 of 46 patients: 12 patients had one-vessel disease, 13 had two-vessel disease, and 15 had three-vessel disease. Resting ventriculograms were normal in 36 of 40 patients. Of 21 patients with anterior (V1-V3) ST elevation, 86% had a left anterior descending (LAD) obstruction and 78% had obstruction proximal to the first diagonal branch. LAD disease occurred significantly more frequently than right and circumflex CAD. There was no anatomic correlation of three persons with lateral (leads V4--6, I or aVL) or 27 patients with inferior-posterior (leads II, III, aVF, Y or Z) exercise-induced ST elevation. Therefore, exercise-induced ST elevation is strongly correlated with CAD but not resting wall motion abnormalities. Further, anterior exercise-induced ST elevation in patients without a previous MI often predicts a significant proximal LAD obstruction.

Adult↗
PubMed1979

Reflex control of the circulation by afferents from skeletal muscle.

Functionally, the pressor reflex, rather than the depressor reflex, appears to be the normal physiologic response to exercise. Available data indicate that chemoreceptors, probably in the form of free nerve endings, are stimulated by local factors, e.g., hypoxia or hyperkalemia. Impulses from these receptors are mediated by group IV afferent nerves to the central nervous system. Then, through efferent sympathetic and parasympathetic nerves, systemic blood pressure, cardiac output, heart rate, and myocardial contractility all increase. The baroreceptors tend to modify the reflex increase in heart rate. The potential significance of local control of the systemic circulation by neural reflexes from skeletal muscle is apparent when one considers that during exercise local control allows both rapid and precise control of the circulation from the metabolically active region of the body. However, the exact role of neural reflexes from skeletal muscle during voluntary exercise still remains to be defined. Clearly, more studies are necessary to elucidate fully their function in the overall control of the circulation in conscious animals and man.

Afferent Pathways↗
PubMedDate not supplied

Static exercise in anesthetized dogs, a cause of reflex alpha-adrenergic coronary vasoconstriction.

The coronary blood flow and vascular resistance responses to static hindlimb exercise were studied in 11 anesthetized dogs after beta- and combined alpha- and beta-adrenergic blockade to determine if this stress causes coronary vasoconstriction. After beta-blockade static exercise increased the blood pressure and double product, but decreased the right and left ventricular (LV) coronary blood flow and increased the coronary vascular resistance. These vascular changes primarily occurred in the epicardial and mid-myocardial but not the endocardial layers of the LV. Following combined alpha- and beta-adrenergic blockade, the systemic hemodynamic and coronary flow and resistance changes were abolished. These data suggest that alpha-adrenergic mediated coronary vasoconstriction occurs during static hindlimb exercise in dogs.

Adrenergic alpha-Antagonists↗
PubMedDate not supplied

Cardiac receptors: their function in health and disease.

Cardiac receptors include both mechanically and chemically sensitive receptors located in atria and in ventricles. Atrial receptors innervated by myelinated vagal afferent fibers reflexly regulate heart rate and intravascular volume. On the other hand, stimulation of ventricular receptors can cause either reflex bradycardia and hypotension or, alternatively, excitation of the cardiovascular system. The former response is mediated by vagal afferents, whereas the latter is mediated by sympathetic (spinal) afferents. Under normal circumstances, cardiac receptors sense changes in wall motion or diastolic pressure and perhaps provide a fine tuning of the cardiovascular system. However, under certain pathological conditions such as coronary ischemia, which cause release of substances such as bradykinin and prostaglandins, there is an exaggerated response of the ventricular receptors. Because these receptors cause a reflex depression of the cardiovascular system and, in particular, induce renal vasodilation, they may protect the heart and kidney by lessening myocardial oxygen requirements and by increasing renal blood flow. In the situation of heart failure both atrial and ventricular receptors are reset and therefore provide for an exaggerated neurohumoral discharge. Finally, patients with aortic stenosis may demonstrate a paradoxical vasodilation and syncope during exercise when there likely is excessive stimulation of left ventricular receptors by the high transmural pressure.

Afferent Pathways↗