The ratio of the first derivative (dP/dt) of a carotid artery pulse to the developed pressure (P), (dP/dt)/P, is an easily measurable, noninvasive index of cardiac contractility even in moderate exercise. We examined the effects of transient cold exposure on cardiac contractility in normal reactors (n = 12) and hyperreactors (an increase in systolic or diastolic pressure >15 mm Hg; n = 6) by using this index. Eighteen healthy participants were subjected to the cold pressor test, which required them to immerse the right hand in chilly water (4 degrees C) for 2 min. Although cold stress maximally increased mean blood pressure during the second minute, it maximally increased heart rate and cardiac contractility after 60 s of immersion in both groups of subjects. Comparing normal reactors and hyperreactors by two-way ANOVA revealed a group x time interaction for heart rate but not for cardiac contractility. These findings suggest that the increase in cardiac contractility during cold-water immersion dose not reflect the levels of heart rate and muscle sympathetic nerve activity, and that the specific responses of cardiac function to a cold pressor test in hyperreactors depends on heart rate rather than cardiac contractility.
In earlier studies we have shown that both the pressure (P) of the carotid artery pulse (CAP) and its first derivative (CAP dP/dt) could be recorded during moderate exercise. To establish that the CAP (dP/dt)/P is a noninvasive substitute for the left ventricular (LV) value, LV (dP/dt)/P, an index of cardiac contractility, we studied CAP (dP/dt)/P under various states of activity in the autonomic nervous system in 12 healthy male subjects. Increased sympathetic nerve activities yielded by passive tilting, emotional load, or cold stress increased CAP (dP/dt)/P significantly (P < 0.05). Increased parasympathetic nerve activity by ocular compression, however, did not significantly affect the value. Moderate exercise at a heart rate of approximately 150 beats.min-1 increased it significantly from 16.7 to 25.2.s-1 in a supine position (P < 0.001) and from 16.6 to 24.8.s-1 in an upright position (P < 0.001). It increased monotonically as heart rate increased, but the slope was steeper when the heart rate was greater than approximately 100 beats.min-1 than it was when the rate was less than 100 beats.min-1. In conclusion, the present study indicated that CAP (dP/dt)/P can be used as a noninvasive index of cardiac contractility even in moderate exercise.
The precentral extension of area 3 as well as the transition between the frontal operculum and insula (area G) comprises the primary gustatory cortex in the subhuman primate, receiving projections from the thalamic taste relay. However, in contrast to the extensive studies that have been carried out on the latter area, only a few taste units in the former area have been recorded. To clarify gustatory coding in area 3, we investigated the taste response properties of neurons in area 3 compared with those in area G in alert monkeys by infiltrating into their mouths seven taste stimuli [0.3 M sucrose (S), 0.1 M NaCl (N), 0.01 N HCl (H), 0.003 M quinine-HCl (Q), 0.1 M monosodium glutamate (MSG), distilled water (W), and orange juice (OR)] and artificial saliva (SA). A larger number of HCl-best units and a smaller number of quinine-best units were found in area 3 than in area G. The onset latency and response duration were significantly shorter in area 3 than in area G. Weighted multi-dimensional scaling showed that area G divided eight stimulants into four classes, i.e. two groups (H-Q-W and S-MSG-OR), N and SA, whereas area 3 divided them into three classes (N-MSG-W-OR, S-Q, and H-SA). This suggested that tastants not separated in area G were separated in area 3, and vice versa. This indicates that both areas complement each other in the representation of taste stimuli, each contributing to taste information processing in a different manner.
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