The difference in blood pressure between upper arm and finger during physical exercise.

A new apparatus which measures the blood pressure in the finger continuously and yet not invasively was tested for its usefulness during exercise. It was compared with upper arm measurements in 23 volunteers during prolonged bicycle ergometry. Simultaneously, a pulse plethysmogram was recorded from another finger of the same arm, whereas in six additional volunteers Doppler measurements were carried out on the radial artery. The results show that finger systolic pressure ceased to rise at about 40% of maximal exercise; the difference with the continuously rising systolic pressure in the upper arm becoming significant at 140 W. At the same time the amplitude of the finger plethysmogram became significantly higher than its initial value, indicating distinct cutaneous vasodilation, whereas the volunteers also became hot and started to perspire. However, the radial artery 'flow', deduced from the Doppler measurements, did not change significantly during exercise. It increased sharply and markedly in the cooling down period. Simultaneously with this increase in flow, HR and both systolic blood pressures fell drastically whereas the plethysmographic amplitude remained about stable at its raised level. The results fit in with the idea that a compromise is achieved between the need for muscle activity and the need for temperature regulation. It is concluded that the Finapres functions well during exercise, but that the systolic pressure in the finger is not representative for its more central counterpart during cutaneous vasodilation. It is argued that opening up of AVAs may contribute to this pressure effect.

Pulse oximetry--principle and first experiences during anesthesia.

Oximetry is a photometric method for simple, non-invasive, and continuous measurement of the O2 saturation (SaO2). The addition of the word "pulse" indicates that, directed by a photo-electric plethysmogram, measurements are only performed during arterial pulsations. It appears from our first experiences with pulse oximetry during anesthesia that each decrease in SaO2 is indicated quickly and reliably. From a practical point of view it is important that the apparatus is connected quickly and easily, and that the O2 saturation is monitored continuously, also in those periods when normally no blood samples are taken. An additional advantage is that by means of the plethysmogram the circulation is also monitored.

The effect of ketamine on the peripheral circulation: a possible sympathetic ganglion blocking effect.

The effects of induction of anaesthesia, endotracheal intubation and surgical stimuli on the systemic and peripheral circulations were studied in three groups of patients. In group KA (n = 8) anaesthesia was induced with ketamine (2 mg kg-1) and alcuronium, supplemented by N2O-O2 alone; in group KAH (n = 9) 0.5% halothane was added to the N2O-O2; and in the control group TAH (n = 8) anaesthesia was induced with a sleep dose of thiopentone and alcuronium, supplemented by N2O-O2 and halothane. The circulation in the finger was monitored by photo-electric plethysmography. Induction produced a significant pressor response in both ketamine groups, but not in the TAH group, while the finger plethysmogram demonstrated peripheral vasodilatation in all three groups. Intubation, on the other hand, elicited a significant pressor response in the TAH and in the KAH group but not in the KA group. The finger plethysmogram, however, always showed peripheral vasoconstriction during intubation in the thiopentone group (TAH) but never in either of the ketamine groups. The results suggest that ketamine exerts a peripheral ganglion blocking effect.

Photo-electric plethysmography as a monitoring device in anaesthesia. Application and interpretation.

The optical principle of photo-electric plethysmography is described and the clinical significance of changes in the amplitude of the plethysmogram discussed. Physiologically, changes in blood volume pulsations depend on the distensibility of the vessel wall as well as on the intravascular pulse pressure. The importance of both factors in the interpretation of changes in the arterial pulse amplitude is illustrated by examples from 500 continuous recordings. In addition, it is shown that changes in the height of ventilatory waves may be of diagnostic significance.

Comparison of plethysmograms taken from finger and pinna during anaesthesia.

Pulse plethysmograms from finger and pinna were recorded simultaneously during anaesthesia, and marked differences in their response to various stimuli recorded. The differences have been illustrated by a number of examples.

Effects of peripheral vasoconstriction on the measurement of blood pressure in a finger.

Using noninvasive techniques only, the fall in mean pressure and the pulse amplification between brachial and finger arterial pressure were measured in six anaesthetised female subjects during surgery. Brachial pressure was measured every 2 min with an oscillometric technique. Finger pressure was measured continuously using an arterial volume clamp method. In addition changes in the degree of peripheral vasoconstriction were established on an adjacent finger with a photo reflection plethysmograph. On the average finger mean pressure is 10 mmHg below brachial pressure. The difference tends to decrease with increasing constriction. The change in the difference between full constriction and maximal dilatation is 8 mmHg. The average finger to brachial pulse amplitude ratio changes from 110% at maximal dilatation to 170% at full constriction. Finger systolic pressure overshoot is responsible for the pulse wave amplification. On the average it is + 7 mmHg and ranges between maximal dilatation and full constriction over 26 mmHg. The standard error deviation on the volume clamp method could be established at 5% for mean pressure, about equal to that of the oscillometric technique in the literature.

Effects of peripheral vasoconstriction on the blood pressure in the finger, measured continuously by a new noninvasive method (the Finapres).

The authors determined whether vasoconstriction alters the ability of a noninvasive method (Finapres) of continuously measuring arterial blood pressure in the finger to function accurately. They compared the response of the Finapres to blood pressures determined simultaneously by an oscillometric technique (Dinamap) in six anesthetized patients. Vasoconstriction was detected from a photoelectric plethysmogram, which was recorded continuously from an adjacent finger. Vasoconstriction was defined as a decrease in amplitude to less than half of its highest value in one and the same patient. From the 378 paired blood pressure readings obtained in this study, 51% took place in such a vasoconstricted state. The authors found that diastolic and mean blood pressures in the finger were, on the average, 9 mmHg below those in the upper arm and that the systolic pressure was 7 mmHg above that in the upper arm. The authors concluded that the Finapres keeps functioning well during peripheral vasoconstriction and is a recommendable method to monitor arterial blood pressure in the finger.

The origin of inverted waveforms in the reflection plethysmogram.

In reflection plethysmography at the finger inverted pulsewaves are sometimes observed, especially when, during anaesthesia, arterial pressure is measured in the same arm with an inflatable cuff. The origin of this inversion is investigated to two series experiments with volunteers. In the first series of experiments the influence of the pressure in the upper arm cuff was investigated and in the second series the influence of the application pressure of the transducer on the finger. It is concluded that inversion of the pulse waves of the plethysmogram is local phenomenon restricted to the reflection method. It is caused by a relative increase in the optical density of the surrounding tissue in relation to the arterial vessels. In the finger it is brought about by venous engorgement and it is dependent on the applied pressure.

Photoelectric plethysmography--some fundamental aspects of the reflection and transmission method.

In photoelectric plethysmography a distinction is made between the reflection methods. Uncertainties still exist, especially regarding the origin of the reflected signal: some investigators attach quantitative value to the amplitude of the plethysmogram. The various findings are reconsidered. Various fluids are pulsatingly pumped through an in vitro circuit. Flow, pressure and volume pulsations are measured, as is the total light intensity detected by a photoelectric plethysmograph with the small variations caused in it by the pulsations in flow. Both phase and amplitude of the resulting plethysmogram are studied and the results compared with those found in vivo at the fingers and auricles. In vitro, the variations in light reflection are in phase with the volume pulsations: this can only be ascribed to reflection by orienting erythrocytes. In vivo, however, the light reflection, like the light transmission, is in anti-phase with the volume excursions, thus eliminating the determinative effect of light reflection by orienting erythrocytes--the strong reflection from surrounding tissues completely dominates reflection from erythrocytes. Since erythrocytes also have absorptive properties, and the light reflection is in anti-phase with the volume excursions, it is concluded that this absorptivity can manifest itself over the strong reflection from surrounding tissue. In vivo, therefore, the reflection plethysmogram is, in principle, an absorption measurement. The relationship between intensity of detected light and resultant voltage may not be linear: this nonlinearity may not be neglected when amplitude changes are compared. Amplitude changes of different plethysmograms may only be compared quantitatively if there is no difference in their light-voltage relationship.