Vascular reactivity in middle cerebral artery and basilar artery by transcranial Doppler in normals subjects during hypoxia.

The anatomical and physiological differences between the carotid and vertebrobasilar circulations suggest the possibility of a different response to variations in systemic pO2. We evaluated cerebrovascular response (CR) in these two systems by monitoring variations in the blood flow velocities in the middle cerebral and basilar arteries during hypoxia. Eighteen healthy, non-smoking volunteers underwent transcranial Doppler study during a state of hypoxia obtained by means of the rebreathing method. Oxyhaemoglobin saturation (SaO2) was monitored using a pulsoxymeter in the 88-94% range. The cerebral blood flow velocity (BFV) was measured in the right middle cerebral artery (MCA) and the basilar artery (BA). Our findings indicate that the mean blood flow velocity (MFV) in the BA changes at a lower rate than that in the MCA during hypoxia.

Correction of hypoxia and hypercapnia in COPD patients: effects on cerebrovascular flow.

To assess the responsiveness of cerebral blood flow to arterial carbon dioxide tension (Pa,CO2), arterial oxygen tension (Pa,O2), and pH modifications, in chronic hypercapnia, we measured middle cerebral blood flow velocity (CBFV) by transcranial Doppler ultrasound in 13 chronically hypercapnic, long-term ventilated patients with chronic obstructive pulmonary disease (COPD), in the following conditions: 1) breathing room air; 2) with oxygen supplementation; 3) during mechanical noninvasive intermittent positive pressure ventilation (nIPPV) with O2 enrichment. Under baseline conditions (room air), the CBFV was within the normal range. During oxygen administration, a statistically significant increase was obtained in Pa,O2 (6.5 +/- 0.6 vs 11.2 +/- 1.9 kPa (49.1 +/- 4.3 vs 84.3 +/- 14.6 mmHg)), without relevant variations in: CBFV (54.2 +/- 9.1 cm.s-1), Pa,CO2 (8.6 +/- 1.0 kPa (64.7 +/- 7.7 mmHg)) and hydrogen ion concentration [H+] (42.9 +/- 2.9 nM), compared to baseline values (CBFV = 52.8 +/- 10.7 cm.s-1; Pa,CO2 = (8.4 +/- 0.9 kPa (63.1 +/- 7.1 mmHg; [H+] = 41.8 +/- 2.8 nM). After nIPPV, Pa,O2 did not increase any further (10.6 +/- 1.7 kPa (79.2 +/- 12.7 mmHg)), while CBFV (40.9 +/- 12.6 cm.s-1), Pa,CO2 (7.5 +/- 1.3 kPa (56.2 +/- 9.4 mmHg)) and [H+] (39.1 +/- 4.6 nM) showed a significant reduction compared to oxygen therapy (p < 0.01). We therefore conclude that in chronically hypercapnic long-term ventilated patients cerebral blood flow depends mainly on changes in Pa,CO2 and [H+], whilst oxygen does not seem to interfere with cerebral flow velocity. The reduction of Pa,CO2, due to mechanical ventilation, may determine cerebral blood vessel constriction, with possible impairment of cerebral functions.

Breathing pattern during and after maximal exercise testing in young untrained subjects and in obese patients.

More rapid and more shallow breathing (RSB) than usual, manifested by a lower tidal volume and greater breathing frequency at a given level of ventilation, may be caused by inspiratory muscle fatigue and pulmonary congestion. It has been observed during recovery in young trained adults after very high exercise levels and in middle-aged patients with cardiac disease, after their maximal work load. We studied the breathing pattern during and after exercise testing up to the maximal work capacity in a group of normal untrained, young people and in a group of young obese subjects. RSB was present in normal subjects after a work load which required a maximal O2 consumption near the theoretical value (93% in our cases) and was not present in obese patients probably because neither inspiratory muscle fatigue, nor pulmonary congestion occurs in these subjects. Maximal heart rate at peak of exercise was significantly higher in normal subjects and a direct correlation between delta Vt and maximal heart rate was found in all normal subjects. This is compatible with the hypothesis that RSB is mainly due to an initial interstitial pulmonary edema, as supposed by other authors.

Cerebral vascular responsiveness in chronic hypercapnia.

To assess the responsiveness of the cerebral vessels to chronic hypercapnia, we measured middle cerebral artery flow velocity by transcranial Doppler ultrasound in 20 normal subjects and in 14 COLD patients before and after stimulation by progressive hypercapnia (rebreathing test) or by intravenous administration of an acetazolamide bolus. The results showed no statistically significant difference in baseline flow velocity between the normal subjects and the COLD patients. The COLD patients showed a reduced cerebral vascular responsiveness to both stimuli. Cerebral blood flow is normal in chronic hypercapnia and the mechanism by which compensation is achieved leads to a decrease in cerebral vascular responsiveness.

Haemorheological effects of fructose-1,6-diphosphate in patients with lower extremity ischaemia.

A prospective, single-blind study was carried out in 30 patients with obstructive peripheral artery disease to investigate the haemorheological properties of fructose-1,6-diphosphate (FDP). Patients were allocated at random to receive 7 to 10-days' treatment with either 10 g or 10% FDP twice daily or saline. Measurements were made on entry and at the end of treatment of whole blood and plasma viscosity, erythrocyte deformability and aggregation, and lower limb blood flow was evaluated by Doppler technique. FDP treatment was associated with a reduction in whole blood viscosity (24%) and red blood cell aggregation index (27%), and an improvement in red blood cell deformability (42%) (p less than 0.01). No significant changes were observed in the control group. Plasma viscosity did not change in either treatment group. Limb blood flow increased (p less than 0.05) only in patients treated with FDP; the improvement was more pronounced in the most severely affected side (30%). No untoward events were observed or reported in any of the patients studied.

[Hemorheologic characteristics in beta-thalassemic homozygotes before and after splenectomy]. / Caratteristiche emoreologiche nella beta-talassemia omozigote prima e dopo splenectomia.

In a group of 36 homozigous beta-thalassaemic children we studied the effect of splenectomy on hemorheologic characteristics. The aim of the work was to evaluate the importance of such operation either on anemia or on erythrocyte deformability. Whole blood viscosity was measured with a Brookfield Microviscometer (LVT) and erythrocyte deformability was evaluated with the erythrocyte filtration technique using policarbonate membranes. The more the erythrocyte deformability decreases, the more the erythrocyte filtration rate decreases. Our data show that splenectomized children, have worse hemorheologic characteristics according to the longer survival time of pathological red blood cells in spite of their reduced deformability. This behaviour can be modified only by blood transfusion that we have seen to be able to reduce whole blood viscosity and to increase erythrocyte filtration rate in splenectomized children. We think that splenectomy must be delayed as long as possible so that hemodinamyc conditions cannot be worsened. An hemorheologic monitorage could be useful for diagnostic and prognostic evaluations both in splenectomized and not splenectomized children.

[Comparison of methods for determining erythrocyte deformability]. / Confronto fra metodiche per la determinazione della deformabilità eritrocitaria.

We have studied the erythrocyte deformability by means of the filtration technique proposed by Reid et al. and with the new technique proposed by Schmid-Schönbein et al. using a Filtrometer MF4. We have studied 50 healthy subjects (24 females and 26 males) aged 25-61 (mean age 34 years). Our results show that slope 80% (SL80) and minimal value (MV) represent the more reliable indexes given by Filtrometer MF4. This instrument gives an exhaustive and automated analysis of erythrocyte deformability. Its results allow us a more extensive knowledge of hemorheological behavior of red blood cells in very low flow conditions.

Effects of isovolumetric venesection on blood viscosity, on red cell deformability, and on arterial flow velocity in chronic respiratory failure with secondary polycythemia.

Normovolemic hemodilution produced by isovolumetric venesection was done in 8 patients with polycythemia and respiratory failure secondary to chronic obstructive pulmonary disease. The 'deformability index' was studied by means of a filtration technique. The blood flow velocity in ascending aorta and right pulmonary artery was also studied by means of ultrasonic Echo-Doppler technique. The procedure showed in all patients an increase of oxygen tension and a decrease of carbonic gas tension in arterial blood. At the same time it was possible to demonstrate an improvement of red cell deformability and an increase of arterial flow velocity. Isovolumetric venesection is an important procedure in the management of patients with polycythemia secondary to respiratory failure.

Effect of hematocrit on the blood viscosity of patients with chronic respiratory failure and secondary polycythemia.

The blood of patients with chronic global respiratory failure and polycythemia exhibits higher viscosity than that of normal subjects. Plasma changes have been excluded as causal factors. The viscosity of whole blood, plasma and blood after correction of hematocrit (Ht; 45%) with autologous plasma, has been determined. The results indicate that in such patients the increase in Ht is not the most important factor affecting the rheological properties (increased viscosity) of blood. A high Ht value may be only pat of the mechanism that increases the blood viscosity of patients with chronic obstructive pulmonary disease. There is evidence that other factors are responsible for increased blood viscosity in chronic respiratory failure.

[Effects of oxygen inhalation therapy on blood and phonomechanography in patients with heart disease, lung disease and cardiorespiratory insufficiency]. / Effetti emogasanalitici e fonomeccanografici della ventiloterapia con ossigeno in pazienti cardiopatici, pneumopatici e con insufficienza cardiorespiratoria.

Arterial PaO2 and some phonomechanographic indices were studied during and after a period of 40-60-100% oxygen breathing in fourteen patients (six with pulmonary insufficiency, four with cardiac disease and four with cardiorespiratory insufficiency). Arterial PaO2 was measured at the beginning, every five minutes during and many times after the ventilation. Myocardial performance was also measured by sistolic time: isovolumetric contraction time, left ventricular expulsive time, preejection pressure, deformation time. The authors discuss the modifications of these indices and the clinical involvement of O2 breathing.