Measurement of local blood flow of the intestine by hydrogen clearance method; experimental study.

Local blood flow of the bowel wall was measured by hydrogen clearance method both in the muscular and submucosal layers in the mongrel dog, separately and concurrently. A platinum wire electrode with a bare tip of 0.5 mm in length and 0.2 mm in diameter was inserted into the each layer. About 10 per cent hydrogen gas was inhalated directly through the side hole attached to the endotracheal tube for 1-2 minutes and the obtained clearance curves were plotted on the semi-logarithmic scale, which was almost monoexponential. The results obtained were as follows: 1) Mean basal perfusion rate of the muscular layer of the intestine was 0.81-0.92 ml/min/gm, whereas that of the submucosal layer was 1.29-1.31 ml/min/gm, respectively. There was little difference of perfusion rates between the small and the large intestine. The results showed good correlationship with those reported by other authors. 2) The effect of vasoactive substances such as vasoconstrictor and vasodilator on the local blood flow in the bowel wall was confirmed. 3) This method is repeatedly applicable for measurement and also renders the information on the distribution of blood flow in the splanchnic area.     

Measurement of regional gastric mucosal blood flow by hydrogen gas clearance

Gastric mucosal blood flow as measured by the hydrogen gas clearance method was compared with total gastric blood flow as determined by venous outflow in an isolated segment of canine stomach. During rest and histamine stimulation, hydrogen gas clearance correlated lineally with total gastric blood flow (p < 0.001). Correlation analysis revealed a slope of 1.21 and a correlation coefficient of 0.97. The slope of 1.21 indicates that the ratio of mucosal to total gastric blood flow was approximately 82 percent. This fractional distribution of blood flow is in agreement with that previously reported by microsphere technique. In the intact stomach of anesthetized rats and dogs, antral mucosal blood flow was significantly higher than that of the corpus. This finding may, in part, contribute to the observation that acute stress erosion occurs predominantly in the corpus of the stomach. Histamine stimulation selectively increased the mucosal blood flow of the corpus, whereas antral mucosal blood flow remained unchanged. As a result, there was no significant difference in mucosal blood flow between the antrum and the corpus during histamine stimulation.     

Measurement of cutaneous blood flow by clearance of hydrogen gas generated by electrolysis

In an attempt to assess the reliability of a method for measurement of local blood flow-namely, the clearance of electrochemically generated hydrogen gas-a series of experiments were conducted using the skin and skin flap in rats and rabbits. The results showed high accuracy in obtained values, good reproducibility in the repeated measurements, and consistency with the values obtained by the hydrogen gas inhalation method. Histological examination revealed only minimal damage to the tissue resulting from the measurement. Using this method, blood flow was measured at different sites on the flap in rats. The critical point of blood flow as measured by this method was thoroughly consistent with the dye distance as well as with the survival length. No injurious effects of the measurement procedure on flap survival were noticed. The present study suggests a wide potential application of this method in plastic surgery because of its high reliability and because no radioactivity is involved.     

Measurement of regional myocardial blood flow. Application of the electrolytic hydrogen clearance method in man

To assess myocardial perfusion intraoperatively and to evaluate the adequacy of coronary bypass grafting, we measured regional myocardial blood flow by the electrolytic hydrogen clearance method in 49 patients. Group I comprised 10 patients with nonischemic heart disease and group II, 39 patients with ischemic heart disease undergoing coronary bypass grafting. Group II was subdivided according to the percent stenosis of the coronary arteries supplying the ventricular regions: group IIa, less than 75% stenosis; group IIb, greater than or equal to 75% stenosis. Mean myocardial blood flows were 154 +/- 7, 145 +/- 5, and 98 +/- 9 ml/min/100 gm in groups I, IIa, and IIb, respectively (p less than 0.01, group IIb versus groups I and IIa). Mean blood flows were 161 +/- 19, 159 +/- 12, 78 +/- 12, and 59 +/- 15 ml/min/100 gm in areas of the left anterior descending coronary artery with less than 50%, 75%, 90%, and 99% stenosis in group II. In areas with a totally occluded left anterior descending coronary artery with collaterals, mean flow was 90 +/- 15 ml/min/100 gm. The mean myocardial blood flows were 40 +/- 7 and 100 +/- 14 ml/min/100 gm in areas with anterior Q wave and non-Q wave infarction, respectively (p less than 0.01). After cardiopulmonary bypass, the mean flow increased from 99 +/- 11 to 150 +/- 7 ml/min/100 gm in the grafted areas in group IIb (p less than 0.01), but it did not change in group I or IIa. The electrolytic hydrogen clearance method provided quantitative evaluation of myocardial perfusion and recovery from hypoperfusion by coronary bypass grafting. This method was especially useful in patients undergoing mammary artery grafting.     

Measurement of liver blood flow by galactose clearance

Low-dose galactose clearance is a new method for measuring functional (nutrient) liver blood flow. In 22 healthy beagle dogs, the mean (+/- SD) blood galactose clearance rate of 311 +/- 93 mL/min was not significantly different from the mean measurement obtained using electromagnetic flow probes (322 +/- 37 mL/min). This shows that galactose clearance can be used to measure liver blood flow in healthy dogs. The 22 dogs were divided into two groups of 11. The first group underwent portacaval shunting and weekly galactose clearance rates were measured until death an average of 6 weeks later. The anticipated fall in liver blood flow was successfully detected by the second week after shunting. This suggests that long-term (week-to-week) changes in liver blood flow can be detected by this method. In the second group, ligation of the common bile duct was used to induce secondary biliary cirrhosis. Galactose clearance was measured weekly for 6 weeks and showed a significant decrease by 6 weeks. At 7 weeks, laparotomy was performed in order to take flow-probe measurements; the galactose clearance rate was also measured. Whereas the two methods were similar at the time of the original operation, 7 weeks after ligation there was a significant difference (p = 0.02) with the rate of liver blood flow as measured by galactose clearance being much lower than the flow rate measured by the electromagnetic flow probes. These findings suggest that in cirrhotic dogs, galactose clearance measures functional or effective (nutrient) liver blood flow whereas the electromagnetic flow probe measures anatomic flow. The effective flow gives a more accurate reflection of perfusion of the hepatocyte by blood.     

Estimation of hepatic blood flow by hydrogen gas clearance

The hydrogen gas clearance technique was evaluated to estimate regional hepatic blood flow. Initially, the H2 gas method was compared to the indocyanine green clearance in mini pigs. The blood flow measured by the H2 gas method (0.49 +/- 0.03 ml/min/gm) was only 39% of the calculated blood flow by the indocyanine green method (1.26 +/- 0.14 ml/min/gm). The blood flow determined by H2 gas decreased to 0.06 +/- 0.04 ml/min/gm after ligation of the hepatic artery. No difference in blood flow was found by simultaneous measurements on the left (0.89 +/- 0.1 ml/min/gm) and right (0.96 +/- 0.13 ml/min/gm) liver lobes in rats. After ligation of the left hepatic artery in the rats, a delayed response to H2 application was present and the determined blood flow (0.14 +/- 0.02 ml/min/gm) was significantly reduced (p less than 0.001) compared with the right liver lobe H2 determined blood flow as a control. No current was generated after ligation of the left hepatic artery and the portal vein indicating that there was no blood flow measured by the gas H2 method. The results indicate that the H2 gas clearance technique may be a method that assesses hepatic arterial liver perfusion rather than estimates total hepatic blood flow. The safety and simplicity of the H2 gas clearance technique may make it suitable for clinical application in serial measurement of hepatic arterial blood flow in man.     

Comparison of blood flow assessment between laser Doppler velocimetry and the hydrogen gas clearance method in ischemic intestine in dogs

Blood flow of the colon and the ileum was measured before and after intestinal devascularization by laser Doppler velocimetry and the hydrogen gas clearance technique in 10 dogs in order to evaluate the clinical usefulness of laser Doppler velocimetry. The submucosal blood flow of the colon and the ileum measured by the hydrogen gas clearance method was significantly decreased, as was the subserosal blood flow of both sites measured by laser Doppler velocimetry. There was a linear relationship between the flow values using the two methods both in the colon (r = 0.7192, p less than 0.001) and in the ileum (r = 0.7646, p less than 0.001). These data suggested laser Doppler velocimetry may be a useful method to assess the degree of intestinal ischemia because of its noninvasiveness and good correlation with submucosal blood flow by the hydrogen gas clearance technique.     

A long term observation of local cerebral blood flow using the hydrogen gas clearance technique

Summary Local blood flow was estimated in the cerebral hemispheres of conscious goats using implanted platinum electrodes and the hydrogen gas clearance technique over periods of several weeks. During the first days of the experiments the blood flow rate was either below 27 ml/100 g/min. or above 40 ml/100 g/min. A gradual decrease in flow was observed over five weeks. The final flow values were between 20 ml/100 g/min. and 30 ml/100 g/min. Carotid injections of serotonin, noradrenalin, or metaoxamine, and inhalation of 5% carbon dioxide produced only insignificant changes in local blood flow. The cause of the slow decrease of flow and the change from a biexponential to a monoexponential curve may be explained by local tissue changes during the observation periods.     

Intraoperative evaluation of coronary bypass grafts by measuring myocardial blood flow using the electrolytic hydrogen clearance method

The regional myocardial blood flow (MBF) was measured in 33 patients who underwent coronary bypass graft surgery in order to evaluate the efficiency of coronary bypass grafts in restoring MBF. MBF was measured by the electrolytic hydrogen clearance method during the coronary bypass surgery. The mean prebypass MBF was 161 +/- 19, 162 +/- 12, 80 +/- 12, 43 +/- 14, 104 +/- 18 ml/min/100 g in segments supplied by the left anterior descending coronary artery (LAD) showing less than or equal to 50 per cent, 75 per cent, 90 per cent, 99 per cent, and 100 per cent stenosis with collaterals, respectively. After bypass grafting of the LAD, the mean MBF increased from 70 +/- 13 and 126 +/- 12 ml/min/100 g to 133 +/- 14 and 163 +/- 9 ml/min/100 g in the segments with and without infarction, respectively. The mean postbypass MBF was 149 +/- 10 and 152 +/- 14 ml/min/100 g in the segments supplied by the LAD bypassed with saphenous vein grafts and mammary artery grafts, respectively. Postbypass MBF was dependent upon the magnitude of myocardial infarction. Measurement of MBF by the electrolytic hydrogen clearance method made it possible to quantitatively evaluate myocardial perfusion at the time of operation. It also provided direct information about the effectiveness of myocardial revascularization.     

Intraoperative evaluation of coronary bypass grafts by measuring myocardial blood flow using the electrolytic hydrogen clearance method

The regional myocardial blood flow (MBF) was measured in 33 patients who underwent coronary bypass graft surgery in order to evaluate the efficiency of coronary bypass grafts in restoring MBF. MBF was measured by the electrolytic hydrogen clearance method during the coronary bypass surgery. The mean prebypass MBF was 161±19, 162±12, 80±12, 43±14, 104±18 ml/min/100 g in segments supplied by the left anterior descending coronary artery (LAD) showing ≦50 per cent, 75 per cent, 90 per cent, 99 per cent, and 100 per cent stenosis with collaterals, respectively. After bypass grafting of the LAD, the mean MBF increased from 70±13 and 126±12 ml/min/100 g to 133±14 and 163±9 ml/min/100 g in the segments with and without infarction, respectively. The mean postbypass MBF was 149±10 and 152±14 ml/min/100 g in the segments supplied by the LAD bypassed with saphenous vein grafts and mammary artery grafts, respectively. Postbypass MBF was dependent upon the magnitude of myocardial infarction. Measurement of MBF by the electrolytic hydrogen clearance method made it possible to quantitatively evaluate myocardial perfusion at the time of operation. It also provided direct information about the effectiveness of myocardial revascularization.     

Focal gastric mucosal blood flow by laser-Doppler and hydrogen gas clearance: a comparative study

We compared focal gastric mucosal blood flow (GMBF) values simultaneously obtained by laser-Doppler flowmetry (LDF) and hydrogen gas clearance (HGC) from the same point in a chambered segment model of the gastric corpus in two sets of experiments (Experiments 1 and 2) involving nine anesthetized dogs (weighing 20-30 kg). We also investigated the feasibility of obtaining a conversion factor for LDF signal to absolute flow values. The GMBF values showed a highly significant linear correlation within individual experiments and for the combined data in experiments 1 (r = 0.7132, P less than 0.0001, n = 37) and 2 (r = 0.5660, P less than 0.0001, n = 61). The combined data did not corroborate a common regression line hypothesis in both experiments (Experiment 1: F = 6.59, P less than 0.0005; Experiment 2: F = 10.57, P less than 0.0005). There was a statistically significant difference between the slopes of the 5 and 4 linear regression lines obtained in Experiments 1 (F = 13.15, P less than 0.0005) and 2 (F = 21.14, P less than 0.0005), respectively. The LDF signal was stable and optical coupling is not a problem in this experimental model. HGC and GMBF values were reliable and highly reproducible within dog measurements. We conclude that LDF and HGC are comparable in the measurement of focal GMBF. Our data, however, did not suggest the existence of a conversion factor for LDF signal to absolute flow values from experiment to experiment. Conversion will have to be within individual experiments. Thus, LDF may only be useful in situations where qualitative changes in focal blood flow are investigated.     

The local blood flow of the rabbit bladder measured by electrochemically generated hydrogen gas

The regional blood flow of the urinary bladder of rabbits was measured by electrochemically generated hydrogen gas. Then the effects of increased bladder capacity, and of systemic administration of scopolamine and neostigmine bromide on regional blood flow were examined. The local blood flow of the rabbit bladder was 75.9 +/- 8.4 ml/100 g/min (mean +/- S.E.) and it decreased by increased bladder capacity. It was also decreased by scopolamine bromide, while it was increased by neostigmine bromide.