The responses of aortic arch and right subclavian baroreceptors to changes of non-pulsatile pressure and their modification by hypothermia

1. A method is described for isolation of the aortic arch and right subclavian-carotid angle in situ in the rabbit and perfusion with Krebs-Henseleit solution or blood under controlled conditions of pressure and temperature.2. The characteristics of the baroreceptors of the aortic arch and right subclavian-carotid angle were studied by recording from single or few-fibre preparations of the left and right aortic nerves respectively. Curbes were plotted to show the relationship between the frequency of baroreceptor impulse activity and intra-aortic pressure during non-pulsatile perfusion under steady-state conditions.3. The aortic arch and right subclavian-carotid angle baroreceptors were found to have similar characteristics. Three types of response of the baroreceptors at the threshold pressure to a steady intra-aortic pressure are described.4. Increasing the intra-aortic pressure increased the frequency of impulses in fibres previously active and caused recruitment of other fibres in multi-fibre preparations. The relationship was linear at low pressures and a point of inflexion occurred at higher pressures in the majority of fibres.5. Lowering the temperature of the perfusate reduced the impulse frequency at any given pressure.6. The curves obtained during stepwise increases and decreases in intra-aortic arch pressure were dissimilar, particularly at the lower end of the pressure range. This phenomenon is probably due to properties of the arterial wall.7. When the aortic arch preparation was excised, changes occurred in the shape of the impulse frequency-pressure curves from baroreceptors in both areas. The point of inflexion was elevated and a higher percentage of fibres failed to reach a point of inflexion in the pressure range studied.     

Comparison of the reflex vasomotor responses to separate and combined stimulation of the carotid sinus and aortic arch baroreceptors by pulsatile and non-pulsatile pressures in the dog

1. In the anaesthetized dog the carotid sinuses and aortic arch were isolated from the circulation and separately perfused with blood by a method which enabled the mean pressure, pulse pressure and pulse frequency to be varied independently in each vasosensory area. The systemic circulation was perfused at constant blood flow by means of a pump and the systemic venous blood was oxygenated by an extracorporeal isolated pump-perfused donor lung preparation.2. When the vasosensory areas were perfused at non-pulsatile pressures within the normal physiological range of mean pressures, the reflex reduction in systemic vascular resistance produced by a given rise in mean carotid sinus pressure was significantly greater than that resulting from the same rise of aortic arch pressure.3. On the other hand, when the vasosensory areas were perfused at normal pulsatile pressures and within the normal physiological range of mean pressures, there was no difference in the size of the reflex vascular responses elicited by the same rise in mean pressure in the carotid sinuses and in the aortic arch.4. Whereas the vasomotor responses elicited reflexly by changes in mean carotid sinus pressure are modified by alterations in pulse pressure, those evoked by the aortic arch baroreceptors through changes of mean pressure are only weakly affected by modifications in pulse pressure. Evidence for this was obtained from single stepwise changes of mean pressure in each vasosensory area during pulsatile and non-pulsatile perfusion, and from curves relating the mean pressure in the carotid sinuses or aortic arch and systemic arterial perfusion pressure.5. The vasomotor response elicited by combined stimulation of the carotid sinus and aortic arch baroreceptors was greater than either response resulting from their separate stimulation.6. When the mean perfusion pressures in the two vasosensory areas are changed together, the curve relating mean pressure to systemic arterial pressure during pulsatile perfusion of the areas is considerably flatter than that for non-pulsatile perfusion.7. Increasing the pulse pressure in the carotid sinuses or aortic arch caused a decrease in systemic vascular resistance, the response elicited from the carotid sinuses being the larger.8. Altering the phase angle between the pulse pressure waves in the carotid sinuses and aortic arch had no effect on systemic vascular resistance.9. In both vasosensory areas, increasing the pulse frequency caused a reduction in systemic vascular resistance.     

The effects of changes of extramural, `intrathoracic', pressure on aortic arch baroreceptors

1. The isolated aortic arch was perfused by a method enabling the mean pressure, pulse pressure and pulse frequency to be varied independently. The preparation was also subjected to phasic and non-phasic changes of extramural pressure.2. The aortic arch baroreceptor impulse activity in single or few-fibre preparations was increased by raising the intra-aortic pressure and by applying a negative extramural pressure at constant intra-aortic pressure.3. Curves relating impulse frequency and negative extramural pressure were similar to those relating impulse frequency to intra-aortic pressure. The effective stimulus to the aortic arch baroreceptors is the transmural pressure resulting from the algebraic difference of the intra-aortic and extramural pressures.4. Rhythmical alterations in extramural pressure caused phasic changes in baroreceptor impulse activity. As the pressure became more negative, the impulse frequency increased and other baroreceptors were recruited.5. During pulsatile perfusion of the aortic arch the maximum impulse activity occurred when the negative phase of extramural pressure coincided with the systolic phase of the perfusion pressure.6. These findings are discussed in relation to the effects of changes of intrathoracic pressure on aortic baroreceptor activity in vivo     

Effects of graded pulsatile pressure on the reflex vasomotor responses elicited by changes of mean pressure in the perfused carotid sinus-aortic arch regions of the dog

1. In the anaesthetized dog, the carotid sinuses and aortic arch were isolated from the circulation and separately perfused with blood by a method which enabled the mean pressure, pulse pressure and pulse frequency to be varied independently in each vasosensory area. The systemic circulation was perfused at constant blood flow by means of a pump and the systemic venous blood was oxygenated by an extracorporeal isolated pump-perfused donor lung preparation.2. We have confirmed our previous observations that under steadystate conditions the vasomotor responses elicited reflexly by changes in mean carotid sinus pressure are modified by alterations in carotid sinus pulse pressure, whereas those evoked by changes of mean aortic arch pressure are only weakly affected by modifications of aortic pulse pressure.3. When the carotid sinus and aortic arch regions are perfused in combination at constant pulse frequency (110 c/min), the relationship between mean carotid sinus-aortic arch pressure and systemic arterial perfusion pressure is dependent on the size of the pulse pressure.4. Increasing the pulse pressure alters the curve relating the mean carotid sinus-aortic arch pressure to systemic arterial perfusion pressure in such a way that the perfusion pressure is lower at a given carotid sinus-aortic arch pressure within the range 80-150 mm Hg. The larger the pulse pressure, up to about 60 mm Hg, the greater the fall in systemic arterial perfusion pressure. Above a mean carotid sinus-aortic arch pressure of about 150 mm Hg, alterations of pulse pressure have little effect.5. There is a family of curves representing the relation between mean carotid sinus-aortic arch pressure and systemic vascular resistance, depending on the pulse pressure.     

Afferent sympathetic nerve fibres with aortic endings.

1. We recorded the electrical impulse activity of thirty-five single afferent fibres with aortic endings isolated from the third to the sixth left thoracic sympathetic rami communicantes of anaesthetized cats. The endings of each fibre were localized by mechanical probing of the opened aorta at the end of each experiment. 2. Twenty-four fibres had a single aortic receptive field. Eleven fibres had several and distinct receptive fields (from two to four): they were usually located in nearby aortic areas or, in addition, in other proximal portions of the arterial tree or in the adjacent pleura and connective tissue. 3. Twenty-nine fibres had conduction velocities ranging between 5 and 27 m/sec (Group Adelta), while six fibres had conduction velocities between 0-2 and 1-2m/sec (Group C). 4. The spontaneous impulse activity was in phase with the aortic pressure pulse and consisted of not more than one impulse per pressure pulse. It was increased during increases in aortic pressure and, conversely, decreased during decreases in aortic pressure. In vivo and post mortem studies showed that these mechanoreceptors had an impulse activity which rapidly adapted during sustained stimuli. They thus seem to signal pulsatile aortic stretch. 5. These aortic sympathetic afferents are likely to be part of a nervous pathway through which pressor reflexes, exhibiting positive feed-back characteristics, can elicited.     

Inotropic responses of the left ventricle to changes in aortic arch pressure in anaesthetized dogs

1. Inotropic changes in the left ventricle in chloralose anaesthetized dogs were determined in response to changes in non-pulsatile pressure perfusing the vascularly isolated aortic arch.2. Inotropic responses were assessed by measuring the maximum rate of change of left ventricular pressure (dP/dt max) in preparations in which heart rate, mean ascending aortic pressure and brachiocephalic (i.e. carotid sinus and cerebral) perfusion pressure were held constant.3. dP/dt max increased (average +43%) when aortic pressure was reduced from a level above that which produced maximum depression of the myocardium to a level below which no further responses could be obtained; responses occurred as aortic arch pressure was changed between 250 and 90 mm Hg.5. In the same preparations changes in the brachiocephalic artery perfusion pressure with aortic arch pressure held constant resulted in similar inotropic responses.6. It is suggested that aortic arch baroreceptors may be of importance in the control of the inotropic state of the heart.     

Augmentation of abdominal organ perfusion during cardiopulmonary bypass with a novel intra-aortic pulsatile catheter pump

BACKGROUND: Current pulsatile pumps for cardiopulmonary bypass (CPB) are far from satisfactory because of the poor pulsatility. This study was undertaken to examine the efficiency of a novel pulsatile catheter pump on pulsatility and its effect on abdominal organ perfusion during CPB. METHODS: Twelve pigs weighing 89+/-11 kg were randomly divided into a pulsatile group (n=6) and a non-pulsatile group (n=6). All animals had a CPB for 120 min, aorta clamped for 60 min, temperature down to 32 degrees C, and a perfusion flow of 60 ml/kg/min. In the pulsatile group, a 21 Fr intra-aortic pulsatile catheter, which was connected to a 40 mL membrane pump, was placed in the descending aorta and activated by a balloon pump driver during the first 90 minutes of CPB until aortic declamping. Hemodynamics, organ blood flow, body metabolism, and blood trauma were studied during experiments. RESULTS: Compared with the non-pulsatile group during CPB, the pulsatile group had a higher systolic blood pressure (p<0.01), higher mean arterial pressure (p<0.05), and higher blood flow to the superior mesenteric artery (p<0.05). The hemodynamic energy, indicated by the energy equivalent pressure (EEP) was higher in the gastrointestinal tract and kidney in the pulsatile group (p<0.01, p<0.01). Abdominal organ perfusion status, as indicated by SvO 2 in the inferior vena cava, was higher in the pulsatile group (p<0.05) 30 min after cessation of CPB. Hemolysis indicated by release of free hemoglobin during CPB was similar in the two groups. CONCLUSION: Applying the pulsatile catheter pump in the descending aorta is effective in supplying the pulsatile flow to the abdominal organs and results in improved abdominal organ perfusion during the ischemic phase of CPB.     

Activity of aortic chemoreceptors during electrical stimulation of the stellate ganglion in the cat

1. In anaesthetized cats, action potentials from aortic chemoreceptors were recorded during electrical stimulation of preganglionic sympathetic fibres to the decentralized right stellate ganglion. The rate of discharge in afferents in the ipsilateral but not in the contralateral aortic nerve increased when stimulus frequency was 4/sec or higher.

2. The post-ganglionic fibres in the stimulated pathway originate in the right stellate ganglion. They leave the ganglion in the caudal limb of the ansa subclavia, and the results suggest that the ipsilateral aortic nerve and its branches distribute sympathetic fibres as well as afferents to aortic bodies.

3. In contrast, the rate of discharge of chemoreceptor fibres in the contralateral aortic nerve fell as blood pressure increased during sympathetic stimulation. Sympathetic pathways to the aortic bodies can maintain or increase chemoreceptor discharge during hypertension elicited by sympathetic activation.

     

Mechanism of stimulation of aortic chemoreceptors by natural stimuli and chemical substances

1. Impulses were recorded in single fibres of aortic chemoreceptors of cats anaesthetized with chloralose. There was no demonstrable difference between the responses of the endings of medullated and non-medullated fibres respectively to any of the natural stimuli, such as hypoxia, reduction in blood pressure, or reduction in O₂ content. This indicates that the generator processes are qualitatively and quantitatively identical at the endings of both types of fibres.

2. Most of the endings were practically silent while ventilating the lungs with air. The maximum frequency of discharge averaged over 4-10 sec while ventilating the lungs with 4% O₂ ranged from 1·5 to 24 impulses/sec; in most fibres (twenty-one out of twenty-six endings) it was less than 12 impulses/sec.

3. All the chemoreceptors tested were considerably stimulated following administration of 0·2 or 2% CO at a time when the O₂ content was greater than 4 ml./100 ml.

4. All the chemoreceptors were markedly and rapidly stimulated following circulatory arrest while the cat was ventilated with air. This stimulation fell considerably within 3 min of circulatory arrest. Very little or no excitation followed circulatory arrest while ventilating the cat with pure N₂. These results suggest that excitation following circulatory arrest is not produced by a metabolite.

5. There was a remarkable difference between the sensitivities of endings of medullated and non-medullated fibres to drugs. The former were either unaffected by relatively large doses of ACh (100-200 μg) or phenyl diguanide, or if they were stimulated, the excitation so produced was much less than that produced in endings of non-medullated fibres. This supports the hypothesis that drugs produce their effects by an action at the regenerative regions of the endings, i.e. regions where the nerve impulse is initiated (Paintal, 1964). It also indicates that ACh is not likely to be a transmitter in the normal processes of excitation of chemoreceptors.

6. A mechanism of stimulation of chemoreceptors not involving metabolites is presented.

     

Studies of Blood-pressure Regulation IV. The Effects of Impulse Train Stimulation of the Carotid-sinus Nerves

The effect of sinus nerve stimulation on the blood pressure and heart rate was studied in dogs. Electrical stimulation of the sinus nerves of both sides was given both in the form of 2 types of intermittent impulse trains and as impulses of constant frequency. The intermittent impulse bursts, which were synchronized with the ECG, comprised 5–50 imp which coincided with systole (150 ms). Comparisons were made between stimulation with a constant frequency and the intermittent types, with the same number of impulses per cardiac cycle. It was found that the maximal blood pressure reduction was already reached at 5–10 imp per cardiac cycle. The difference between stimulation with a constant frequency and the intermittent types, with the same number of impulses per cardiac cycle, is negligible as regards blood pressure reduction but the intermittent type has a greater effect on the heart rate. Sinus nerve stimulation in massive haemorrhage and the influence of the amplitude of the stimulation signal were also studied.     

The importance of flow pulsatility for the rate of transvascular fluid filtration in lungs.

1. The rate of transvascular fluid filtration has been studied with a gravimetric technique in isolated perfused rabbit lungs during periods of elevated left atrial pressure (PLA). 2. Fluid filtration was expressed as the filtration coefficient, Kf (g/min x 100 g bloodless lung x mmHg PLA) and determined during alternately pulsatile and non-pulsatile perfusion in six zone III and three zone II/I lung preparations. Perfusion pattern was changed without interruption of flow. Mean in- and outflow pressures were kept constant. 3. In all the lungs it was found that Kf was higher during pulsatile than during non-pulsatile flow (P less than 0.01). Mean Kf (+/- S.E. of mean) for the zone III preparations was 0.42 (+/- 0.089) and 0.27 (+/- 0.057) for pulsatile and non-pulsatile perfusion, respectively. The corresponding figures for the zone II/I preparations were 0.11 (+/- 0.035) and 0.04 (+/- 0.030). 4. We suggest that the difference is due to a larger filtration area and/or a higher mean microvascular hydrostatic pressure during pulsatile than during non-pulsatile flow and not to a rise in hydraulic conductivity due to pressure pulsations ('stretched pores'). 5. When the water-exchange function of the lung is considered, flow pattern should be taken into account as an entity in its own right in addition to the steady state or the mean component of blood flow.     

Afferent fibres from pulmonary arterial baroreceptors in the left cardiac sympathetic nerve of the cat

1. Afferent discharges were recorded from the left cardiac sympathetic nerve or the third sympathetic ramus communicans of anaesthetized cats. Twenty-one single units with baroreceptor activity were obtained.2. The receptors of each unit were localized to the extrapulmonary part of the pulmonary artery, determined by direct mechanical probing of the wall of the pulmonary artery after death of the animals. Conduction velocity of the fibres ranged from 2.5 to 15.7 m/sec.3. Afferent discharges occurred irregularly under artificial ventilation. The impulse activity was increased when pulmonary arterial pressure was raised by an intravenous infusion of Locke solution, or by occlusion of lung roots, and decreased by bleeding the animal from the femoral artery.4. Above a threshold pressure, discharges occurred synchronously with the systolic pressure pulse in the pulmonary artery. A progressive further rise in pressure did not produce an increase in the number of impulses per heart beat. Occlusion of lung roots initially elicited a burst of discharges but the number of impulses for each cardiac cycle gradually decreased.5. The receptors responded to repetitive mechanical stimuli up to a frequency of 10/sec, but failed to respond to stimuli delivered at 20/sec.6. The results provide further evidence for the presence of afferent fibres in the cardiac sympathetic nerve. These afferent fibres are likely to provide the spinal cord with specific information only on transient changes in pulmonary arterial pressure.     

The reflex effects of alterations in lung volume on systemic vascular resistance in the dog

1. The reflex effects of alterations in lung volume on systemic vascular resistance have been studied in anaesthetized dogs under conditions in which the systemic circulation was perfused at constant blood flow. The pressures in the isolated perfused carotid sinuses and aortic arch, and the arterial blood P_O2 and P_CO2 were maintained constant.

2. A maintained inflation of the lungs produced by injection of air into the trachea caused a fall in systemic arterial perfusion pressure, indicating vasodilatation. The size of the systemic vasodilator response varied directly with the pressure and volume of gas used to inflate the lungs. A similar effect was observed when the tidal volume of lungs ventilated by an intermittent positive pressure was increased.

3. Collapse of the lungs by creating a pneumothorax in closed-chest spontaneously breathing animals evoked a systemic vasoconstrictor response which was reversed when the lungs were re-expanded.

4. These vasodilator responses were abolished by dividing the pulmonary branches of the thoracic vagosympathetic nerves. Evidence is presented that the afferent fibres run in the cervical vagosympathetic nerves and through the stellate ganglia.

5. The responses were unaffected by atropine, but were abolished by hexamethonium, guanethidine and by bretylium tosylate, indicating that they are mediated via the sympathetic nervous system.

6. Evidence is presented that the lungs are a constant course of afferent impulses inhibiting the `vasomotor centre', and that the lung inflation—systemic vasodilator reflex is a potential mechanism operating in eupnoeic breathing.

     

Inotropic changes in the left ventricle: the effect of changes in heart rate, aortic pressure and end-diastolic pressure

1. Under conditions where heart rate, mean aortic pressure and enddiastolic pressure in the left ventricle are held constant, the intravenous infusion of isoprenaline is accompanied by large changes in dP/dt max in the left ventricle.

2. Under similar conditions, during stepwise increments in the rate of infusion of isoprenaline the changes in dP/dt max (measured at a constant paced heart rate) were proportional to changes in the free (intrinsic) heart rate. It is concluded that dP/dt max is a quantitative index of inotropic changes in the left ventricle.

3. In comparison to dP/dt max, three other variables which have been used to indicate inotropic changes in the heart (peak pressure in the left ventricle, duration of systole and stroke work at constant end-diastolic pressure), were shown to be unreliable indices of inotropic changes.

4. Using dP/dt max to indicate inotropic changes, alteration in the heart rate while mean aortic pressure and end-diastolic pressure in the left ventricle were held constant, and in mean aortic pressure while heart rate ane end-diastolic pressure in the left ventricle were held constant, were each shown to be accompanied by small inotropic changes in the heart.

5. Under similar conditions, changes in end-diastolic pressure in the left ventricle alone were not accompanied by inotropic changes as indicated by dP/dt max.

     

Cardiovascular risks related to increased diastolic, systolic and pulse pressure. An epidemiologist's point of view.

Since the introduction of the sphygmomanometer at the beginning to the 20th century, the significance of diastolic (DBP), Systolic (DBP) and pulse pressure (PP) as hypertensive cardiovascular risk factors has been controversial. These historical controversies are reviewed. Initially, DBP was thought to be the best measure of risk, but more recently both SBP and DBP, which ever is higher, are used in classifying hypertensive cardiovascular risk. There are problems with the present guidelines, in that SBP and DBP represent only two inflection points on the propagated pulse wave that is measured by cuff readings at the peripheral brachial artery. The heart is exposed to the central aortic pressure not to the brachial artery pressure. Moreover, both peripheral vascular resistance and large artery stiffness contribute to hypertensive cardiovascular risk. In middle-aged and elderly, elevated SBP is a better surrogate measurement of resistance than DBP, but SBP underestimates large artery stiffness. PP, the difference between peak SBP and end DBP, is the single best blood pressure surrogate for large artery stiffness. Epidemiological studies over the past decade point to SBP and DBP as the best cardiovascular risk markers for young subjects, whereas PP takes over as the more powerful risk marker for middle-aged and elderly subjects. These findings support the concept that cardiovascular events are more related to the pulsatile stress of large artery stiffness during systole than the steady-state stress of small vessel resistance during diastole. Therefore, at similar elevations of SBP, subjects with isolated systolic hypertension are at greater risk for cardiovascular events than those with combined systolic/diastolic hypertension.     

Pulmonary O2 transfer during pulsatile and non-pulsatile perfusion

The importance of the perfusion pattern for the oxygen transfer has been examined in isolated rabbit lungs perfused with plasma at constant volume inflow. The lungs were ventilated with constant tidal volume and constant end-expiratory pressure. Following a standardized rise in F_1,0,2 the rate of rise in pulmonary venous P_O2, (ΔP_O2/Δt) was measured during alternately pulsatile and non-pulsatile perfusion in normal lungs and in lungs made edematous by elevation of left atrial pressure. In normal lungs there was no difference in ΔP_O2/Δt when the two modes of perfusion were compared. In edematous lungs ΔP_O2/Δt was statistically higher during pulsatile perfusion, indicating a beneficial effect of flow- and pressure pulsations, e.g. a better distribution of V/Q ratios throughout the lungs. In a separate series of expts. the advancement of a high O₂ front through the airways was measured, and the two perfusion patterns compared. Since no difference was found, we suggest that the phenomenon of “cardiogenic gas mixing” in the airways in vivo is a result of a direct action of the heart on the lungs rather than arterial pulsations.     

Time domain analysis of the arterial pulse in clinical medicine

The arterial pulse at any site is created by an impulse generated by the left ventricle as it ejects blood into the aorta, together with multiple impulses travelling in the opposite direction from reflecting sites in the peripheral circulation. The compound wave at any site depends on the pattern of ventricular ejection, the properties of large arteries, particularly their stiffness (which determines rate of propagation) and the distance to and impedance mismatch at reflecting sites. Physicians are familiar with waveform analysis in the time domain, as in the electrocardiogram (ECG) where the principal features are explicable on the basis of atrial depolarisation followed by ventricular depolarisation, then repolarisation. Effects of cardiac functional and structural disease can be inferred from the ECG. It is more difficult to make similar interpretations from the pulse waveform and clinicians usually use this only to count heart rate, extremes of the pressure pulse to express systolic and diastolic pressure, and (sometimes) time from wave foot to incisural notch to measure time of systole and diastole. More information can be gleaned from the shape of the arterial pressure wave through consideration of the factors which create it—on stiffening of large arteries with age, effects of drugs on smallest arteries, and changes in such arterial properties on left ventricular load and function. Such is a major challenge to future physicians. It is aided by better and more accurate methods for measuring flow and diameter as well as pressure waveforms, and by appropriate use of other analytic techniques such as analysis of the pulse in the frequency domain. Michael F. O’Rourke is a founding director of AtCor Medical, manufacturer of systems for analysing the arterial pulse.     

Influence of intravenous saline infusion on the aortic baroreceptor and left atrial B-type receptor activity in dogs

Influence of i.v. saline infusion on aortic arch pressure, left atrial mean pressure, heart rate, and the time-related characteristics of aortic arch baroreceptor and left atrial B-type receptor activities were studied in 20 beagle dogs. Saline infusion induced tachycardia in 10 dogs and bradycardia in 10. Aortic arch and left atrial pressures increased in both HR response groups. The average discharge rate of baroreceptors increased in both HR response groups, while the duration of baroreceptor burst, the number of baroreceptor action potentials/heart cycle and the average burst frequency did not increase significantly in the group that responded with tachycardia but increased significantly in the group that responded with bradycardia. The number of left atrial B-type action potentials/heart cycle, the average discharge rate and average burst frequency increased in both HR response groups. We conclude that the duration of baroreceptor burst, baroreceptor average burst frequency and the number of baroreceptor impulses/cardiac cycle are the important parameters eliciting baroreceptor reflex to i.v. saline infusion.     

基于电磁驱动的体外膜肺氧合搏动式泵血系统

根据电磁学原理建立梯度线圈-永磁体模型,本研究设计了一款新型电磁驱动搏动式血泵,主要包括驱动装置、泵头装置、冷却系统以及体外循环管路等.搏动式血泵运动速率接近正常人体心率,模仿心脏的节律跳动,产生搏动式血流,实现了搏动式泵血.通过搭建实验平台,采集基于电磁驱动的体外膜肺氧合(extracorporeal membran...     

The spatial selectivity of the visual cells of the cat

1. Micro-electrode recordings have been made from single units in the visual cortex of the cat, during stimulation by moving grating patterns generated on a cathode ray tube.

2. The responses of the units have been measured in terms of either the frequency of impulses, or the contrast sensitivity, and expressed as a function of the spatial frequency of the grating pattern.

3. The amplitude of the responses recorded from cortical cell bodies was dependent upon the orientation of the moving grating, and for these units the stimulus was always presented at the preferred orientation. The response amplitude of other units did not depend upon the orientation of the grating stimulus, and these are believed to be the terminations of geniculate fibres.

4. The high spatial frequency end of the response function measured in terms of the contrast sensitivity could be well fitted by an exponential function. Subtraction of the blank count from the impulse frequency data gave a curve fitted by the same exponential function. The low frequency end was less consistent.

5. The spatial frequency at which this exponential function had fallen by one log. unit was taken to specify the position of the unit's response in the spatial frequency spectrum. For all units these values cover a range of four octaves of spatial frequency (from 0·18 to 3·8 cycles per degree).

6. It is suggested that these neurophysiological results support psychophysical evidence for the existence in the visual system of channels, each selectively sensitive to a narrow band of spatial frequencies.