No abstract

Intravenous digoxin offers no substantial advantages over placebo in recent onset atrial fibrillation with respect to conversion, and provides weak rate control.

This study examined the integrative changes of blood pressure (BP) and stroke volume (SV) leading to the initial biphasic heart rate (fc) response (first 15 s) in simulated diving manoeuvres with and without breathholding (BH). Simulated diving was studied in ten young healthy volunteers by application of a gel-filled pack at 0 degree C and 18 degrees C on the forehead with and without BH. Beat-by-beat and second-to-second fc, BP, SV, and total peripheral vascular resistance (TPR) were followed by continuous non-invasive monitoring. In all conditions (BH with forehead cooling at 0 degree and 18 degrees C) there was an early rise in BP triggering the first tachycardial response (fc acceleration) which was immediately counteracted by the concurrent further increase of SV leading to the second phase of early bradycardic response (fc deceleration). Furthermore, the continuous beat-by-beat and second-to-second monitoring allowed the documentation of a highly significant increase of TPR within the first few seconds of the manoeuvres. Our data further indicated that the differences in haemodynamics observed during the stimuli at different temperatures was overruled by BH. Detailed comparisons of the beat-by-beat and second-to-second analyses were unable to show that one method was better than the other. Using continuous non-invasive monitoring of haemodynamic variables during simulated diving manoeuvres it was possible to provide better insights into the physiological principles and meaning of the diving reflex in humans.

Nebivolol (R67555), a drug with beta 1 receptor antagonizing properties, was administered once daily (5 mg) for 7 days in 10 healthy volunteers. The hemodynamic parameters were measured noninvasively during postural changes (supine, sitting, standing) and during isometric handgrip at 50% maximal voluntary contraction, before and 3, 8, and 23 hours after the first nebivolol intake of 5 mg; the same measurements were done 23 hours after the last intake. Nebivolol lowered arterial blood pressure acutely and chronically due to a decrease in heart rate and cardiac output. The stroke volume seemed to be preserved, while the total peripheral vascular resistance did not change. Nebivolol did not change the orthostatic responses, except that the absolute value was lowered. Nebivolol was unable to prevent the blood pressure increase during isometric handgrip. However, this blood pressure increase was obtained by an increase in the total peripheral vascular resistance and not by an increase in the cardiac output, as observed during control measurements before nebivolol intake.

It has been documented that placing an ice-bag on the forehead causes similar cardiac and vascular responses as face immersion. There has been disagreement concerning the contribution of separate cold stimulation on the face and breathholding in the diving response. This study set out to unravel the extent to which these two factors contribute individually to the observed cardiovascular changes during the combined manoeuvre. It further aimed to reveal whether peripheral vascular responses to these stimuli are different in forearm and calf. We observed a significant rapid increase in the RR-interval, which was maintained until the end of the 25-s observation period and a homogeneous vasoconstriction in forearm and calf, despite minor changes in arterial blood pressure, during breathholding, placing the icebag on the forehead and the combined stimuli. Cardiac and peripheral vascular responses to the combined manoeuvre did not differ significantly from the responses elicited by the two stimuli separately. This test is another example that illustrates the heterogeneous cardiovascular response involving both parasympathetic and sympathetic activation. Moreover, since the icebag on the forehead test is technically easy to perform and does not require the active co-operation of the patient, it may be a valid method to replace a full face immersion test accompanied by breathholding.