Non-invasive measurement of brain temperature using radiometric thermometry: experimental validation and clinical observations in asphyxiated newborns

BACKGROUND

Therapeutic hypothermia (HT) has been shown to decrease death and severe disability in infants with hypoxic-ischemic encephalopathy (HIE). Rectal temperature (RT) is used to determine the temperature set-points for treatment with HT, however experimental studies have shown significant differences between RT and brain temperature during HT. Knowledge of actual brain temperature during HT might allow better determination of optimal degree of cooling and improve outcomes.

OBJECTIVES

To compare measurements of brain temperature obtained by non-invasive radiometric thermometry (RadT) to direct tissue measurements in an experimental model of HT, and to use RadT in newborn infants with HIE undergoing HT.

STUDY DESIGN

RadT measurements of brain temperature were compared to fiber optic (Luxtron) thermometry measurements placed at a depth of 1.5 centimeters into the brain of cooled miniswine. Following validation studies, brain RadT and RT measurements were continuously recorded in thirty infants with HIE during HT and rewarming.

RESULTS

RadT and Luxtron probe temperatures were comparable in miniswine throughout a temperature range similar to therapeutic HT. RadT measurements of brain temperature were higher than RT in 60% of infants with HIE undergoing HT. Higher RadT measurements compared to RT were associated with cerebral white matter abnormalities (p = 0.01).

CONCLUSIONS

RadT provides a safe, passive and non-invasive way to measure brain temperature that can be used in the clinical setting. RadT may be helpful in determining the optimal degree of cooling and identifying infants at highest risk of brain injury.

Adenosine prevents PMA-induced lung injury via an A2 receptor mechanism

Previous studies indicate that adenosine attenuates phorbol myristate acetate-(PMA) induced canine lung injury, but the mechanism has not been explained. To evaluate adenosine's protective mechanism, isolated and blood-perfused dog lungs were challenged by PMA (50 micrograms) under control conditions and after both pre- and post-treatment with adenosine and pretreatment with 2-chloro-N6-cyclopentyladenosine (CCPA), 2-[p-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamido adenosine (CGS 21680C), 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; PD-116948), or isoproterenol. Injury was assessed by measurement of the capillary filtration coefficient (Kf,c), and pulmonary vascular resistance was measured. PMA increased the Kf,c (0.170 +/- 0.015 to 1.030 +/- 0.167 ml.min-1.cmH2O-1.100 g lung wet wt-1) and the total pulmonary vascular resistance (18.2 +/- 3.8 to 110.2 +/- 60.8 cmH2O.l-1.min.100 g lung wet wt). Pretreatment with adenosine, A2 agonist, A1 antagonist, and isoproterenol blocked the increase in Kf,c induced by PMA. These agents also slightly attenuated the resistance increase induced by PMA, with the exception of the A1 antagonist, which completely prevented the resistance increase (24.3 +/- 7.8 to 23.4 +/- 8.1 cmH2O.l-1.min.100 g lung wet wt). The A1 agonist also slightly attenuated the increase in Kf,c (0.174 +/- 0.022 to 0.486 +/- 0.128 ml.min-1.cmH2O-1.100 g lung wet wt-1) and did not affect the resistance increase. Posttreatment with adenosine did not significantly affect the changes induced by PMA. These data show that PMA-induced increases in capillary permeability in the isolated blood-perfused dog lung can be blocked by pretreatment with adenosine, which binds the adenosine A2 receptors.

Initial treatment of pulmonary edema: a physiological approach

An understanding of the physiological principles involved in lung fluid balance is useful in the initial treatment of pulmonary edema. Normally, a very small volume of fluid is filtered from the pulmonary vasculature into the interstitial space. This interstitial fluid enters the pulmonary lymphatics and is transferred to mediastinal lymphatics at an estimated rate of 20 ml/hr. Under abnormal circumstances, fluid filtration may occur at such a rapid rate that it overwhelms the lymphatics and interstitial space and results in alveolar flooding. This may occur as a result of increased pulmonary vascular pressure or increased vascular permeability. The two general goals of initial therapy are (1) to relieve hypoxemia and (2) to reduce pulmonary capillary pressure. Relieving hypoxemia may require the use of supplemental oxygen by nasal prongs or mask, continuous positive airway pressure (CPAP) mask, or even endotracheal intubation and mechanical ventilation. Measures to decrease preload and thereby reduce pulmonary capillary pressure include sitting the patient up, administering a loop diuretic or morphine intravenously, and in some circumstances using sublingual nitroglycerin. After initial treatment is underway, a search for and specific management of the underlying cause of pulmonary edema can proceed.

Effect of ischemia reperfusion or hypoxia reoxygenation on lung vascular permeability and resistance

The effect of ischemia reperfusion or hypoxia reoxygenation on pulmonary vascular permeability and resistance was studied in 25 isolated blood-perfused dog lungs. Vascular permeability, assessed by determining filtration coefficient (Kf), and vascular resistances were measured at the beginning and end of the experiment. Ischemia reperfusion was produced by occluding blood flow to the lung for 3 h and reperfusing for 1 h, whereas hypoxia reoxygenation was obtained by ventilating the lung with 95% N2-5% CO2 for 3 h and then ventilating with 95% O2-5% CO2 for 1 h with no interruption of perfusion. There was a significant increase in Kf in both ischemia reperfusion and hypoxia reoxygenation groups (51 and 85%, respectively), and total vascular resistance increased greatly in both groups (386 and 532%, respectively). Two additional groups were also studied in which the ischemia reperfusion or hypoxia reoxygenation lungs were pretreated with allopurinol (20 micrograms/ml). The Kf did not significantly increase in either the allopurinol ischemia reperfusion or the allopurinol hypoxia reoxygenation groups (22 and 6%, respectively). However, total vascular resistance significantly increased in both groups (239 and 224%, respectively). Although vascular permeability is modestly increased by both ischemia reperfusion and hypoxia reoxygenation, the predominant change in these conditions is the increased vascular resistance, which predominantly affects the postcapillary resistance and would result in a greater tendency for edema to develop in these slightly damaged lungs. Allopurinol, which inhibits xanthine oxidase, attenuated the permeability changes in both groups and may be useful in preventing ischemia reperfusion injury in certain conditions.

Endotoxin extends survival of adult mice in hyperoxia

Research on endotoxin protection from oxygen toxicity is presently limited to the rat model since only rats have been protected by endotoxin. This study reports that endotoxin also extends survival of adult male mice in hyperoxia (greater than 99% oxygen at 1 ATA). Initially, 4-month-old male mice were treated with Boivin-extracted E. coli endotoxin and placed in hyperoxia. Zymosan-primed mice receiving 2 or 10 micrograms endotoxin, and unprimed mice receiving 10-40 micrograms endotoxin, showed moderate protection against hyperoxia; 11/15 Boivin-treated mice survived 120 hours exposure to hyperoxia with time-of-death in hyperoxia = 126.7 +/- 4.4 hours (mean +/- SEM, n = 15). This contrasts with untreated male mice; 0/4 survived 120 hours exposure to hyperoxia with mean survival = 103.5 +/- 3.5 hours. Mice receiving 20 or 60 micrograms Westphal-extracted endotoxin were not protected nor were older female mice receiving 20 micrograms Boivin-extracted endotoxin. This study suggests that age, sex, the extraction method used to obtain endotoxin, and possibly the time of year when endotoxin is administered, are important variables in allowing endotoxin to extend survival of mice in hyperoxia.

Endotoxin protection of rats from pulmonary oxygen toxicity: possible cytokine involvement

Treatment with endotoxin protects rats against lung injury during hyperoxia (greater than 98% oxygen at 1 atmosphere absolute for 60 h). This study demonstrates that serum from endotoxin-treated donor rats also protects recipients from oxygen toxicity. Rats treated with serum from saline-treated donors were not protected, and protection was not explained by residual endotoxin in protective sera. Unlike endotoxin-protected rats (where lung antioxidant enzyme activity is elevated after hyperoxia), postexposure superoxide dismutase (SOD) and catalase (CAT) activities in the lungs of serum-protected rats were not affected. Levels of tumor necrosis factor (TNF) and interleukin 1 (IL-1) in protective sera were increased. This study demonstrates that increases in lung SOD and CAT activity are not required for endotoxin protection from hyperoxia and suggests that TNF and IL-1 may participate in the mechanism of endotoxin protection.

Normal airway responsiveness to methacholine in cardiac asthma

Cardiac asthma has been used as a synonym for episodes of cough, dyspnea, and wheezing caused by left ventricular dysfunction. The similarity of the terms bronchial asthma and cardiac asthma, and the observed symptoms of each disease implies a common pathophysiology. Bronchial asthma is characterized pathologically by airway narrowing, inflammation, edema, and obstruction by mucus. Bronchial asthma is defined as increased responsiveness of the tracheobronchial tree, which is manifested clinically as reversible expiratory airflow obstruction. The classic symptoms of bronchial asthma are cough, dyspnea, and wheezing. Cardiac asthma produces the same symptoms, but the pathophysiology producing these symptoms is not well described. We describe two patients with cardiac asthma who failed to demonstrate airway hyperresponsiveness to nonspecific bronchoprovocation testing and we postulate that these patients' symptoms were produced exclusively by left ventricular failure.

Pulmonary vascular permeability and resistance measurements in control and ANTU-injured dog lungs

Because questions have arisen regarding pulmonary vascular permeability and resistance measurements in isolated, perfused lungs, we sought to determine the 1) stability of repeated measurements of permeability and resistance in control lungs; and 2) magnitude of change in these measurements when permeability was greatly increased. Using blood-perfused dog lungs, we measured filtration coefficient (Kf) and isogravimetric capillary pressure (Pci) as indexes of vascular permeability, and we also determined total vascular resistance (Rt) as well as the segmental resistances using the double-occlusion pressure (Pdo). In a control group (n = 8), the base-line measurement of Kf (0.21 +/- 0.02 ml.min-1.cmH2O-1.100 g-1) and Pci (10.2 +/- 0.9 cmH2O) did not change over 4 h, indicating no changes in endothelial barrier function. Base-line Rt (13.9 +/- 2.6 cmH2O.l-1.min.100 g) also did not significantly increase. In a second group (n = 5), alpha-naphthylthiourea (ANTU) increased the initial Kf more than eight times (from 0.17 +/- 0.03 to 1.40 +/- 0.32 ml.min-1.cmH2O-1.100 g-1) and decreased Pci by 56% (from 9.4 +/- 0.6 to 4.1 +/- 0.4 cmH2O) at 1 h, indicating severely damaged endothelium. In addition, the Pdo determined during isogravimetric conditions correlated very well with Pci not only in control lungs (observed previously) but also in very permeable lungs (not previously reported). We conclude that this experimental model provides an excellent means of assessing changes in pulmonary microvascular permeability, with a spectrum ranging from no changes in hourly measurements for 4 h to obvious changes in permeability by 1 h.

Protective effects of O2 radical scavengers and adenosine in PMA-induced lung injury

We have previously shown that phorbol myristate acetate (PMA) produces acute lung injury in blood-perfused lungs but not in plasma-dextran-perfused lungs. This is compatible with the concept that its major mechanism of injury is the stimulation of O2 radicals by neutrophils, which in turn increase permeability by damaging the endothelial cells. In this study we measured vascular permeability and resistance before and 1 h after PMA in five groups of blood-perfused dog lungs: PMA alone in one group and pretreatment with catalase, superoxide dismutase, deferoxamine, and adenosine each in four other groups. By the use of two indexes of permeability, the filtration coefficient and the isogravimetric capillary pressure, we found that, compared with PMA alone, catalase, deferoxamine, and adenosine provided significant protection, whereas the results with superoxide dismutase were variable. These four drugs also significantly attenuated the marked increased resistance seen with PMA alone. Although the effects seen with the first three can be explained by their scavenging of O2 radicals, adenosine appears to provide protection through a separate mechanism.

Changes in the pulmonary capillary pressure after cardiac surgery

The changes in the pulmonary circulation in 37 cardiac surgery patients undergoing coronary artery bypass (CABG), n=16; aortic valve replacement (AVR), n=13; and mitral valve replacement (MVR), n=8 were studied. The visual technique for the determination of pulmonary capillary pressure (Pc) was used in the preoperative and postoperative periods. The ratio of Pc to the pulmonary artery wedge pressure (Pw) was calculated to determine whether Pc and Pw varied independently. In addition, total pulmonary vascular resistance (PVR) was divided into precapillary (ra) and postcapillary (rv) components. Results from the CABG patients showed that the relationship between Pc and Pw remained constant despite an increased cardiac output. This differs from the data obtained from AVR and MVR patients in whom the Pc/Pw ratio was significantly higher after surgery. Therefore, Pw would underestimate Pc in this group of patients. In addition, MVR patients showed a significant postoperative increase in PVR and rv as compared with their preoperative values. This was also significantly higher than the rv in either AVR or CABG patients. The etiology of this change is unknown.

Attenuation of permeability lung injury after phorbol myristate acetate by verapamil and OKY-046

Phorbol myristate acetate (PMA), which produces an experimental model of acute lung injury similar to the adult respiratory distress syndrome, was studied in isolated dog lung lobes perfused at constant pressure in Zone 3 conditions. The effect of 25 to 50 micrograms PMA on pulmonary vascular permeability and resistance was observed in 4 groups of lungs: Group 1, perfused with a plasma/dextran solution; Group 2, perfused with blood; Group 3, blood-perfused and pretreated with verapamil (a calcium channel blocker); and Group 4, blood-perfused and pretreated with OKY-046 (a thromboxane synthetase inhibitor). Permeability changes were assessed by determining capillary filtration coefficient (Kf), isogravimetric capillary pressure (Pci), and in blood-perfused lungs, the protein reflection coefficient (sigma d). An increase in Kf, a decrease in Pci, and a decrease in sigma d, all indicative of an increase in vascular permeability, occurred 1 h after PMA in blood-perfused but not in plasma/dextran-perfused lungs. An increase in pulmonary vascular resistance occurred in both blood- and plasma/dextran-perfused lungs. Verapamil (2 X 10(-5) M) and OKY-046 (7 X 10(-4) M) pretreatment in blood-perfused lungs essentially blocked the PMA-induced change in permeability and significantly attenuated the increased vascular resistance. Total leukocyte and platelet counts fell in all blood-perfused lungs, whether pretreated or not. We conclude that cellular components of blood (platelets and/or leukocytes) are required to produce the permeability injury but not the pulmonary vasoconstriction and that the injury can be attenuated by either a calcium channel blocker or a specific thromboxane synthetase inhibitor. The left ventricular volume change caused by increasing right ventricular volume was measured at normal and elevated pericardial pressures.

Pulmonary edema. Complication in the management of sickle cell pain crisis

Over a 12-month period, there were 51 admissions for sickle cell pain crisis. Of these, the course of four patients (two with hemoglobin SS, one with hemoglobin SC, and one with hemoglobin S-Thal) was complicated by the development of pulmonary edema. Pulmonary edema complicating the management of sickle cell pain crisis has not previously been described. Vigorous fluid replacement with hypotonic saline and parenteral narcotic analgesics are conventional modalities of therapy, but may contribute to the development of pulmonary edema. Narcotic analgesics causing increased permeability are well established. In pulmonary vascular beds predisposed to injury, hypotonic saline administration causing an increased hydrostatic pressure and decreased oncotic pressure may further compound pulmonary edema development. On the basis of the experience in this study, a conservative approach to the use of fluid administration and narcotic analgesics is advised.

Nuclear magnetic resonance of perfused tissue

The effect of perfusion on the NMR signal observed in NMR imaging is studied in a phantom and in two isolated perfused canine lungs. It is observed that perfusion in tissue has little effect on longitudinal relaxation times. Transverse relaxation rates are observed to correlate linearly with rates of perfusion, in accordance with a model presented.

Measurement of effective pulmonary capillary pressure using the pressure profile after pulmonary artery occlusion

Pulmonary artery catheters are frequently used to measure pulmonary vascular pressures, particularly the pulmonary wedge pressure (Pw), which reflects pulmonary venous and ideally left atrial pressures. However, the pulmonary capillary pressure (Pc) is the major force in the formation of pulmonary edema. Unfortunately, Pw has been interpreted as being identical to Pc. In this study we used 7-Fr pulmonary artery catheters to measure effective Pc in closed-chest animals and patients. The decreasing pressure profile after pulmonary artery occlusion was separated into fast and slow components, with the inflection point between them representing Pc. Pc was also estimated by mathematically analyzing the curves in terms of a precapillary resistance, a large pulmonary capillary capacitor, and a postcapillary resistance. In dogs, Pc was determined after pulmonary vascular resistance had been increased by infusing serotonin and histamine. While Pw remained unchanged, serotonin increased pulmonary artery pressure (Ppa) 52% and Pc 16%, whereas histamine increased Ppa only 25%, but increased Pc by 35%. This is consistent with studies showing that serotonin primarily elevates precapillary resistance, and histamine increases postcapillary resistance. In thoracic surgery patients, Pc was not consistently related to Pw. This measurement was simple, reproducible, and provided a more precise capillary filtration pressure than Pw. It should be clinically useful in monitoring patients with pulmonary hypertension and adult respiratory distress syndrome, especially those with pulmonary artery catheters.

Thermodilution measurement of lung water

The detection and measurement of pulmonary edema by the thermal-dye method appears to be accurate and reproducible under specified laboratory conditions. The ETV, which represents the difference in distribution volumes of the diffusible (thermal) indicator and the intravascular (green dye) indicator, should closely estimate the ELM (ETV = 0.984 ELM). Experimental measurements of ETV have shown a very good correlation with ELM, with a tendency for overestimation in normal lungs and underestimation in severely edematous lungs. In contrast to previous measurements using isotopic water methods, thermal-dye measurements have revealed that the estimation of ELM by ETV in severe edema (alveolar flooding) does not plateau. The limitations of the thermal-dye technique reflect the evenness of lung perfusion. Depending on their size and number, emboli produce perfusion defects and reduce ETV. Airway injury also reduces ETV, apparently by redistribution of blood flow. Alterations of ETV by hemodynamic factors suggest that reduction in perfusion pressure may be more significant than changes in flow, although more data are needed. Atelectasis without a reduction in blood flow does not decrease ETV. PEEP may increase ETV when lung injury is not uniform, perhaps by redistributing blood flow, and this maneuver may be useful in detecting underestimation of ELM. Position of the thermistor produces the greatest degree of variability by distorting the thermodilution curve and prolonging the MTT. This results in an increased ETV and an overestimation of ELM. In laboratory studies, the measurements of ETV can be validated by gravimetric analyses of lung water. Since this method of validation is not possible in clinical studies, measurements of ETV in patients must be interpreted in light of limitations demonstrated in the laboratory. Suggestions for avoiding the most common errors in measuring ETV are listed in Table 3.

Effects of histamine, serotonin, and norepinephrine on circulation of dog lungs

The action of histamine (H), serotonin (5-HT), and norepinephrine (NE) on the lung vasculature was evaluated in isolated blood-perfused dog lung lobes using isogravimetric techniques. Pre- and postcapillary resistances, isogravimetric capillary pressure (Pc,i), capillary filtration pressure (Pc,f), capillary filtration coefficient (Kf,c), and vascular pressure-volume relationships were measured. For constant-flow conditions, all drugs induced marked increases in both pre- and postcapillary resistances and increased Pc,f. The rise in Pc,f was most pronounced for H and least marked for NE and 5-HT. For constant-pressure perfusion, Pc,f increased slightly for H but not for NE and 5-HT, while total vascular resistance increased 4-5 times for all drugs. Vascular distensibility and volumes decreased markedly for NE and 5-HT but only slightly for H. None of the drugs appeared to alter capillary permeability because Kf,c and Pc,i measured during the infusions were not different from control.

Effect of edema and hemodynamic changes on extravascular thermal volume of the lung

The extravascular thermal volume of the lung (ETV) has been measured in dogs as the difference between mean transit time (t) volumes for heat and indocyanine green dye across the pulmonary circulation, calculated as the product of thermal dilution cardiac output (CO) and the difference in t for aortic indicator-dilution curves generated by right and left atrial injections. ETV measurements were compared with the extravascular lung mass (ELM): in 21 normal dogs, ETV/ELM = 1.11 +/- 0.14 (SD); in 17 dogs with hydrostatic pulmonary edema (up to 21 g/kg), ETV/ELM = 0.90 +/- 0.11; and in 27 dogs with alloxan pulmonary edema (up to 51 g/kg); ETV/ELM = 0.93 +/- 0.13. For all 65 dogs the mean ETVELM was 0.98 +/- 0.15, and the liner regression was ETV (ml/kg) = 0.90 ELM (g/kg) + 0.86 +/- 2.25 (SEE; r = 0.96). Calculations based on measurements of lung specific heat predict that ETV/ELM should equal 0.984. With acute changes in pulmonary hemodynamics, ETV was reduced by reductions in pulmonary arterial pressure (Ppa) sufficient to produce zone 1 conditions at the top of the lung. However, ETV was not affected by increases in CO (mean = 50%) produced by nitroprusside or by increases in Ppa and pulmonary blood volume (mean = 27%) produced by partial mitral valve obstruction. Distortion of the thermal dilution curve due to position of the arterial thermistor appears to be the greatest source of variability and overestimation. Simultaneous measurements from pairs of thermistors differed by 14% (range 0.4-50%).

Effect of air embolism on the measurement of extravascular lung thermal volume

To determine the accuracy of thermal-dye indicator-dilution measurements of lung water during perfusion abnormalities, we embolized air into the lungs of 10 dogs anesthetized with pentobarbital and mechanically ventilated. A control period was followed by a period of air injection (10 ml) and subsequent air infusion (E1), a second period of air injection and infusion (E2), and a recovery period. Thermal and dye-dilution curves were obtained during each period, and cardiac output (CO), total thermal volume, intravascular volume, and extravascular thermal volume (ETV) were calculated. Pulmonary arterial pressure (Ppa) increased from 16 +/- 2 cmH2O during control to 29 +/- 3 cmH2O during E1 and to 40 +/- 3 cmH2O during E2 and decreased to 21 +/- 2 cmH2O during recovery. CO did not change, and pulmonary vascular resistance changed in a pattern similar to Ppa. ETV fell from 113 +/- 8 ml during control to 59 +/- 11 ml during E1 and to 29 +/- 9 ml during E2 and rose to 136 +/- 23 ml during recovery. There was no increase in extravascular lung water or mass determined gravimetrically at the end of the experiments. We conclude that the thermal-dye technique will underestimate lung water in nonedematous lungs if emboli prevent complete diffusion of the thermal indicator.

Edema affects intra-alveolar fluid pressures and interdependence in dog lungs

The pressures in occluded, fluid-filled segments of lung were measured in closed-chest supine dogs ventilated with positive pressure at a constant tidal volume. Segment fluid pressures decreased in response to lung inflation and were used with esophageal and airway pressures to calculate an index of bronchiolar-parenchymal interdependence. Animals were subjected to three sequential 5% body wt infusions of Tyrode's solution followed by a 20- to 30 min-recovery period after each infusion. The interdependence index decreased significantly following each infusion, with infusions as small as 1% body wt producing a detectable decrease. The mean pressures in the Tyrode's solution-filled segments generally increased in response to the infusions, but the time course of the response was variable. The base-line pressure in Tyrode's solution-filled segments was -4.8 +/- 2.4 cmH2O. This increased to -1.1 +/- 2.7 cmH2O after a total of 15% body wt had been infused. At the same time, extravascular lung water increased by approximately 17%. Thus negative collapse pressures in the occluded segments were opposed by mechanical stresses transmitted through alveolar wall attachments. This counterbalancing stress was consistently reduced by both increased tissue hydration and increased pulmonary vascular pressure.

Role of platelet serotonin in the canine pulmonary response to endotoxin

There is evidence suggesting a role for platelet serotonin (5-HT) in the immediate pulmonary response to endotoxin in the dog (J. Appl. Physiol. 23: 47, 1967). To further define this role, autologous canine platelets were labeled with 5-[14C]HT in vitro and then reinfused. Subsequently Escherichia coli endotoxin (0.55:B-5, Difco), 2.5 mg/kg, was injected. Within 5 min dynamic compliance (CL) fell by more than 50%, and nonelastic resistance (RL) increased by more than 200%. Despite a 95% decrease in platelet count, less than 10% of the platelet 5-HT was released as determined by changes in the radioactivity of platelet-poor plasma (PPP) prepared from both aortic and pulmonary artery blood. As a positive control, injected of bovine collagen produced a similar decrease in platelet count that was associated with a significant increase in the radioactivity of aortic and pulmonary artery PPP. FInally, rapid injection of a dose of 5-HT equivalent to 25% of the 5-HT in circulating platelets did not cause a change in CL or RL equivalent to that produced by endotoxin. From these data we conclude that endotoxin injection does not cause immediate massive platelet activation and that platelet 5-HT does not play a major role in the immediate pulmonary response to endotoxin.

Effect of methysergide on the acute lung mechanics response to endotoxin

The effect of the serotonin antagonist methysergide on the acute lung mechanics response to endotoxin in anesthetized, paralyzed, mechanically ventilated dogs was investigated. In five dogs given 0.25 mg/kg Escherichia coli endotoxin only, the pulmonary nonelastic resistance (RL) increased to 238% of control and dynamic compliance (CL) decreased to 50% of control. In a second group of five dogs, methysergide (0.25 mg/kg) was shown to markedly attenuate the lung mechanics response to serotonin (0.04 mg/kg), which alone had produced changes in lung mechanics greater than endotoxin. In these same dogs endotoxin administered after injection of methysergide produced an increase in RL to 377% and a decrease in CL to 33% of control. In a third group of five dogs whose lung mechanics response to serotonin was also greater than to endotoxin alone, endotoxin administered after injection of saline produced an increase in RL to 168% and a decrease in CL to 58% of control. Since the response to endotoxin after injection of methysergide exceeded the response after saline, we conclude that serotonin is not a mediator of the acute lung mechanics response to endotoxin.

Immunological status as a criterion for operability of genitourinary cancers

Delayed hypersensitivity reaction of 116 consecutive cases of urologic cancers were studied by skin tests. Ninety-one percent of those who were operable or free of diseases at least six months had positive skin reaction. All patients with inoperable or recurrent bladder, kidney, or testis tumor had negative skin reaction. All patients with operable prostatic cancer and 52% of those with inoperable prostatic cancer had positive skin reaction. Skin testing could provide useful data regarding the extent of tumor and operability. It is proposed that skin testing be included in routine preoperative evaluation of urologic cancers.