Tolerance of the isolated perfused lung to hyperthermia

Pulmonary ventilation and gas exchange during prolonged exercise in humans: Influence of dehydration, hyperthermia and sympathoadrenal activity

NEW FINDINGS

What is the central question of the study? Ventilation increases during prolonged intense exercise, but the impact of dehydration and hyperthermia, with associated blunting of pulmonary circulation, and independent influences of dehydration, hyperthermia and sympathoadrenal discharge on ventilatory and pulmonary gas exchange responses remain unclear. What is the main finding and its importance? Dehydration and hyperthermia led to hyperventilation and compensatory adjustments in pulmonary CO2 and O2 exchange, such that CO2 output increased and O2 uptake remained unchanged despite the blunted circulation. Isolated hyperthermia and adrenaline infusion, but not isolated dehydration, increased ventilation to levels similar to combined dehydration and hyperthermia. Hyperthermia is the main stimulus increasing ventilation during prolonged intense exercise, partly via sympathoadrenal activation.

ABSTRACT

The mechanisms driving hyperthermic hyperventilation during exercise are unclear. In a series of retrospective analyses, we evaluated the impact of combined versus isolated dehydration and hyperthermia and the effects of sympathoadrenal discharge on ventilation and pulmonary gas exchange during prolonged intense exercise. In the first study, endurance-trained males performed two submaximal cycling exercise trials in the heat. On day 1, participants cycled until volitional exhaustion (135 ± 11 min) while experiencing progressive dehydration and hyperthermia. On day 2, participants maintained euhydration and core temperature (Tc ) during a time-matched exercise (control). At rest and during the first 20 min of exercise, pulmonary ventilation (V ̇ E ${\skew2\dot V_{\rm{E}}}$ ), arterial blood gases, CO2 output and O2 uptake were similar in both trials. At 135 ± 11 min, however,V ̇ E ${\skew2\dot V_{\rm{E}}}$ was elevated with dehydration and hyperthermia, and this was accompanied by lower arterial partial pressure of CO2 , higher breathing frequency, arterial partial pressure of O2 , arteriovenous CO2 and O2 differences, and elevated CO2 output and unchanged O2 uptake despite a reduced pulmonary circulation. The increasedV ̇ E ${\skew2\dot V_{\rm{E}}}$ was closely related to the rise in Tc and circulating catecholamines (R2  ≥ 0.818, P ≤ 0.034). In three additional studies in different participants, hyperthermia independently increasedV ̇ E ${\skew2\dot V_{\rm{E}}}$ to an extent similar to combined dehydration and hyperthermia, whereas prevention of hyperthermia in dehydrated individuals restoredV ̇ E ${\skew2\dot V_{\rm{E}}}$ to control levels. Furthermore, adrenaline infusion during exercise elevated both Tc andV ̇ E ${\skew2\dot V_{\rm{E}}}$ . These findings indicate that: (1) adjustments in pulmonary gas exchange limit homeostatic disturbances in the face of a blunted pulmonary circulation; (2) hyperthermia is the main stimulus increasing ventilation during prolonged intense exercise; and (3) sympathoadrenal activation might partly mediate the hyperthermic hyperventilation.

Low-field thoracic magnetic stimulation increases peripheral oxygen saturation levels in coronavirus disease (COVID-19) patients: A single-blind, sham-controlled, crossover study

ABSTRACT

Severe acute respiratory syndrome coronavirus-2 may cause low oxygen saturation (SpO2) and respiratory failure in patients with coronavirus disease (COVID-19). Hence, increased SpO2 levels in COVID-19 patients could be crucial for their quality of life and recovery. This study aimed to demonstrate that a 30-minute single session of dorsal low-field thoracic magnetic stimulation (LF-ThMS) can be employed to increase SpO2 levels in COVID-19 patients significantly. Furthermore, we hypothesized that the variables associated with LF-ThMS, such as frequency, magnetic flux density, and temperature in the dorsal thorax, might be correlated to SpO2 levels in these patients.Here we employed an LF-ThMS device to noninvasively deliver a pulsed magnetic field from 100 to 118 Hz and 10.5 to 13.1 milliTesla (i.e., 105 to 131 Gauss) to the dorsal thorax. These values are within the intensity range of several pulsed electromagnetic field devices employed in physical therapy worldwide. We designed a single-blind, sham-controlled, crossover study on 5 COVID-19 patients who underwent 2 sessions of the study (real and sham LF-ThMS) and 12 patients who underwent only the real LF-ThMS.We found a statistically significant positive correlation between magnetic flux density, frequency, or temperature, associated with the real LF-ThMS and SpO2 levels in all COVID-19 patients. However, the 5 patients in the sham-controlled study did not exhibit a significant change in their SpO2 levels during sham stimulation. The employed frequencies and magnetic flux densities were safe for the patients. We did not observe adverse events after the LF-ThMS intervention.This study is a proof-of-concept that a single session of LF-ThMS applied for 30 minutes to the dorsal thorax of 17 COVID-19 patients significantly increased their SpO2 levels. However, future research will be needed to understand the physiological mechanisms behind this finding.The study was registered at ClinicalTrials.gov (Identifier: NCT04895267, registered on May 20, 2021) retrospectively registered. https://clinicaltrials.gov/ct2/show/NCT04895267.

Isolated lung perfusion for pulmonary metastases, a review and work in progress

Pulmonary metastasectomy is a widely accepted treatment for many patients with pulmonary metastases from various solid tumors. Nevertheless, 5–year survival is disappointing, with rates of 25–40%, and many patients develop recurrences. Isolated lung perfusion (ILuP) is a promising new technique to deliver high–dose chemotherapy to the lungs, while minimising systemic toxicities. This procedure is technically safe and feasible; however, clinical value and efficacy remain unclear. The aim of this paper is to give a review of literature on ILuP in humans, and to describe the development of the perfusion procedure in our institute.

Isolated Lung Perfusion for Pulmonary Metastases

Isolated lung perfusion (ILP) is a surgical technique developed to treat pulmonary metastases. During ILP, high-dose chemotherapy is delivered into the pulmonary vasculature, minimizing systemic exposure and delivering the chemotherapeutic agent directly to the lung. ILP has been studied extensively in a variety of animal models and in humans in phase I trials. The most frequently studied chemotherapeutic agents used in ILP are doxorubicin, 5-flurodeoxyuridine, tumor necrosis factor-α, paclitaxel, melphalan, gemcitabine, and cisplatin. Phase I clinical trials with ILP have shown that ILP can be safely performed in humans but with mixed clinical results and poor long-term survival.

Isolated lung perfusion for pulmonary metastases

Isolated lung perfusion is an experimental surgical technique evaluated for the delivery of high-dose chemotherapy to improve 5-year survival after pulmonary metastasectomy. Extensive experimental work in animal models has demonstrated superior pharmacokinetics and efficacy compared with systemic therapy. Phase I clinical trials of isolated lung perfusion found a maximum tolerated dose**** of TNF-alpha, doxorubicin, cisplatin, and melphalan, whereas the combination of isolated lung perfusion with a complete metastasectomy was feasible. The combination of isolated lung perfusion and regional lung perfusion techniques needs further investigation.

Isolated lung perfusion for the treatment of pulmonary metastases current mini-review of work in progress

Surgical resection of lung metastases is a widely accepted procedure but long-term results are disappointing with a 5-year survival rate of approximately 40%. Pulmonary metastasectomy is only indicated when complete resection can be achieved. A better survival is reported in patients with a single metastasis or a disease-free survival of more than 3 years. Intravenous chemotherapy has no major impact on survival because high-dose therapy is limited by systemic side-effects. Isolated lung perfusion has the advantage of both selectively delivering an agent into the lung while diverting the venous effluent. This allows the drug to be given in a significantly higher dose compared to intravenous therapy, while drug levels in critical organs are kept low enough to avoid significant morbidity. Isolated lung perfusion has proven to be effective for the treatment of lung metastases in animal models while the procedure is technically safe in humans. However, the real clinical value and survival benefit remain to be determined in ongoing clinical trials.The aim of this paper was to update the literature on isolated lung perfusion for the treatment of lung metastases. Furthermore, some proposals are made in order to improve the ultimate prognosis of these patients.

Effects of Ventilation on Lung Function after Normothermic Ischemia

The effects of atelectasis and hyperinflation were compared on immediate postischemic lung function and architecture, following normothermic ischemia. Thirty Sprague-Dawley rats were divided into 3 groups; 2 groups were subjected to 60 minutes of normothermic ischemia. The lungs were atelectatic in 10 (group A), they were hyperinflated to a pressure of 10 cm H2O in 10 (group B), and 10 rats served as nonischemic controls (group C). After 5 minutes of reperfusion, left pneumonectomies were performed and the lungs were examined histopathologically. There were no statistically significant differences in pulmonary venous blood oxygen tension or pH in the 3 groups. There was a significant difference between the compliance data of groups A and B (p < 0.05) and a highly significant difference between the compliance data of groups A and C (p < 0.001). Alveolar edema, perivascular edema, peribronchiolar edema, vascular congestion, and intrapulmonary hemorrhage were more frequent and more severe in the atelectatic group than in the hyperinflated group. The results indicate that postischemic injury occurred at an early stage in atelectatic lungs before any change in blood gas values and that superior postischemic preservation was achieved in lungs maintained in a hyperinflated state.

Transit time dispersion in the pulmonary arterial tree

Knowledge of the contributions of arterial and venous transit time dispersion to the pulmonary vascular transit time distribution is important for understanding lung function and for interpreting various kinds of data containing information about pulmonary function. Thus, to determine the dispersion of blood transit times occurring within the pulmonary arterial and venous trees, images of a bolus of contrast medium passing through the vasculature of pump-perfused dog lung lobes were acquired by using an X-ray microfocal angiography system. Time-absorbance curves from the lobar artery and vein and from selected locations within the intrapulmonary arterial tree were measured from the images. Overall dispersion within the lung lobe was determined from the difference in the first and second moments (mean transit time and variance, respectively) of the inlet arterial and outlet venous time-absorbance curves. Moments at selected locations within the arterial tree were also calculated and compared with those of the lobar artery curve. Transit times for the arterial pathways upstream from the smallest measured arteries (200-micron diameter) were less than approximately 20% of the total lung lobe mean transit time. Transit time variance among these arterial pathways (interpathway dispersion) was less than approximately 5% of the total variance imparted on the bolus as it passed through the lung lobe. On average, the dispersion that occurred along a given pathway (intrapathway dispersion) was negligible. Similar results were obtained for the venous tree. Taken together, the results suggest that most of the variation in transit time in the intrapulmonary vasculature occurs within the pulmonary capillary bed rather than in conducting arteries or veins.

Isolated lung perfusion with melphalan for the treatment of metastatic pulmonary sarcoma

OBJECTIVE

Isolated lung perfusion allows the delivery of high-dose chemotherapy to the perfused lung and is an efficacious modality in the treatment of pulmonary metastases in the rat. Melphalan activity in this model was investigated.

METHODS

TOXICITY STUDY: Maximum tolerated dose of melphalan delivered by means of isolated lung perfusion was determined by survival after contralateral pneumonectomy. PHARMACOKINETICS STUDY: Nineteen rats were treated with melphalan administered either by isolated lung perfusion (2 mg) or intravenously (2 mg or 1 mg). Lung, pulmonary effluent, and serum melphalan were analyzed by high-pressure liquid chromatography. EFFICACY STUDY: On day 0, 41 rats received an intravenous injection of 5 x 10(6) methylcholanthrene induced sarcoma cells. On day 7, rats either received intravenous melphalan (2 mg [n = 10]; 1 mg [n = 8]) or underwent left isolated lung perfusion with 2 mg of melphalan (n = 12). Isolated lung perfusion with buffered hetastarch in sodium chloride (Hespan, n = 11) was used as control. On day 14, pulmonary nodules were counted.

RESULTS

TOXICITY

Maximum tolerated dose of melphalan delivered buy means of isolated lung perfusion was 2 mg.

PHARMACOKINETICS

Left lung melphalan level was significantly higher in the isolated lung perfusion group (62.2 +/- 34.3 microg/gm lung) than in the intravenous treatment groups (6.9 +/- 1.9 microg/gm lung and 3.3 +/- 0.9 microg/gm lung, respectively) (p = 0.0002).

EFFICACY

Significantly fewer left lung nodules were found in animals receiving melphalan by means of isolated lung perfusion (7 +/- 10) than in the groups receiving intravenous melphalan (60 +/- 21) or buffered hetastarch by isolated lung perfusion (84 +/- 52) (p = 0.01 and p = 0.0001, respectively).

CONCLUSION

Isolated lung perfusion with melphalan is safe and effective in the treatment of pulmonary sarcoma metastases in the rat.

Isolated lung perfusion with platinum in the treatment of pulmonary metastases from soft tissue sarcomas

A multimodality approach including operation and isolated lung perfusion with platinum was used in six patients with lung metastases from soft tissue sarcomas. Staged thoracotomies were used in two patients with bilateral lesions. The inclusion criteria generally applied for surgical excision were adopted in this study. The pulmonary artery and a portion of the left atrium were isolated from systemic circulation and cannulated. The cannulas were then connected to a perfusion circuit and normothermic isolated lung perfusion was done for 60 minutes. The lung was then flushed and metastasectomy was done. Serial blood (systemic and pulmonary), tissue (normal lung and tumor), and urine samples were obtained for platinum content measurement by flameless atomic absorption spectroscopy. Lung damage was assessed by light and electron microscopy examination and by serial respiratory tests. Isolated lung perfusion was accomplished in all patients without any death, operative complication, or systemic toxicity. After operation, interstitial and alveolar edema developed in two patients (48 hours after treatment), necessitating respiratory support in one case. Total platinum concentrations in pulmonary plasma were about 43 times greater than those in systemic plasma. No differences in platinum concentrations between normal lung and metastatic tissue were found. Thus the proposed isolated lung perfusion technique is feasible and safe enough to be offered as a valid model to study combined chemosurgical approaches in the treatment of lung metastases.

Isolated lung perfusion with tumor necrosis factor for pulmonary metastases

BACKGROUND

A phase I trial was initiated to define the feasibility and safety of single-lung isolation perfusion with tumor necrosis factor-alpha, interferon-gamma, and moderate hyperthermia for patients with unresectable pulmonary metastases.

METHODS

Twenty patients with lung metastases (Ewing's, 2; sarcoma, 8; melanoma, 6; other, 4) were considered for single-lung isolation perfusion with 0.3 to 6.0 mg of tumor necrosis factor-alpha and 0.2 mg interferon-gamma delivered through an oxygenated pump circuit. Sixteen perfusions were performed in 15 patients (bilateral in 1). Metastases were completely resected (no single-lung isolation perfusion) in 3 patients, 1 patient had extrapulmonary disease, and one single-lung isolation perfusion was aborted for mechanical reasons.

RESULTS

There were no significant changes in systemic arterial blood pressure or cardiac output during perfusion. Systolic pulmonary artery pressure increased with isolation, but returned to pre-single-lung isolation perfusion levels after clamp release. The maximum systemic tumor necrosis factor-alpha level was 8 ng/mL, whereas pump-circuit levels ranged from 200 to 10,976 ng/mL. There were no deaths, and the mean hospitalization period was 9 days (range, 5 to 34 days). A short-term (6 to 9 month) unilateral decrease in perfused nodules was noted in 3 patients (melanoma in 1, adenoid cystic carcinoma in 1, renal cell carcinoma in 1).

CONCLUSIONS

Future studies using a combination of biologic modifiers, chemotherapy, and hyperthermia should be pursued to define active cytotoxic agents that will preserve underlying pulmonary function.

Lung perfusion with chemotherapy in patients with unresectable metastatic sarcoma to the lung or diffuse bronchioloalveolar carcinoma

Eight patients with metastatic sarcoma to the lung (n = 4) or diffuse bronchioloalveolar carcinoma of the lung (n = 4) underwent isolated lung perfusion with chemotherapy in a pilot study. Ages ranged from 18 to 60 years and half were female. The left lung was perfused in three patients (single lung perfusion) and both lungs in five patients (total lung perfusion). Perfusions ranged from 45 to 60 minutes at ambient or normothermic temperatures. One patient received perfusion at moderate hyperthermia (40 degrees C). Escalating doses of doxorubicin (1 to 10 micrograms/ml perfusate) was used in six patients, whereas two received cisplatin (14 and 20 micrograms/ml perfusate). There were two major complications and no objective responses. The isolated perfusion systems gave excellent separation between systemic and pulmonary circulations with zero to 15% of the measured peak drug concentration of the pulmonary perfusate detected in the systemic circulation. Drug concentrations in normal lung and tumor generally increased with higher drug dosages and drug was detectable in mediastinal lymph nodes of three out of four patients in whom sampling was done. Isolated lung perfusion with chemotherapy can be done safely in patients with lung malignancies and evidence suggests that higher drug dosages should be well tolerated.

Isolated lung perfusion with tumor necrosis factor: a swine model in preparation of human trials

Isolated lung perfusion with tumor necrosis factor (TNF) potentially could deliver high doses of drug and avoid systemic toxicity in patients with unresectable lung cancer or metastases. We investigated the feasibility of isolated lung perfusion with TNF in a pig model. Eleven animals had left-sided isolated lung perfusion with no TNF (n = 3), 40 micrograms/kg TNF (n = 2), 80 micrograms/kg TNF (n = 3), and 40 micrograms/kg TNF at moderate (39.5 degrees C) hyperthermia (n = 3). Hemodynamic monitoring and measurement of systemic and pulmonary circuit TNF levels were performed. Surviving animals were electively sacrificed a minimum of 6 months after isolated lung perfusion. All sham-perfused pigs survived. Isolated lung perfusion elevated pulmonary artery pressure, decreased cardiac output, and had minimal effects on mean pressure (15 +/- 0 versus 32 +/- 8 mm Hg, 4.5 +/- 1.1 versus 3.03 +/- 0.03 L/min, 67 +/- 11 versus 61 +/- 2 mm Hg; before versus after 90 minutes of isolated lung perfusion). Both 40 micrograms/kg animals and 2 of the 3 hyperthermic perfusion pigs survived, with 1 requiring pneumonectomy. Of the three 80 micrograms/kg animals, 1 survived, 1 died, and 1 required pneumonectomy. Survivors, compared with dying animals, had lower systemic/pulmonary TNF ratios and lower peak systemic TNF levels. All surviving pigs were electively sacrificed. These data justify phase I human protocols of isolated lung perfusion with TNF and hyperthermia; however, intraoperative leak rates must be monitored to ensure pulmonary isolation because systemic TNF levels may dictate treatment morbidity/mortality.