Wound healing after tissue injury by CO2 laser beam

A study of tissue healing (liver, kidney, and lungs) after injury by a CO₂ laser beam revealed no marked leukocytic infiltration of tissues bordering on the injury. The absence of inflammatory changes during healing is evidence that resorption of injured tissues and proliferation of tissue cells accompanied by inflammation are relatively independent processes and do not constitute a single pathogenetic chain of repair.Department of Pathological Anatomy, A. V. Vishnevskii Institute of Surgery, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. I. Strukov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 88, No. 10, pp. 463–465, October, 1979.     

Responses of human cutaneous afferents to CO2 laser stimuli causing pain

Summary Microelectroneurographic studies in man allow the comparison of stimulus induced activity in the single peripheral nerve unit with the subject's ratings of sensation. Relationships between stimulus intensity, single unit discharges, and pain ratings were investigated using a CO₂ laser stimulator which delivers radiant heat pulses of 50 ms duration. Recordings were performed percutaneously from the radial nerve at the wrist. Receptor types were identified by their response to different stimulus modalities and by their reaction delay to electrical test stimuli within the receptive field. Receptive fields of identified units were stimulated with randomised series of different radiant heat intensities between half and double the individual pain threshold (5 to 20 W; stimulation area 64 mm²).The largest receptor class observed to be activated by CO₂ laser stimuli were polymodal C-nociceptors. None of them was spontaneously active. High discharge rates up to 75/s were not necessarily associated with pain but, if pain was felt, the impulse trains usually lasted for more than 60 ms. Inter-spike intervals were distributed over a wide range between 8 and 145 ms with a peak at about 25 ms. This peak was only slightly shifted by increasing the stimulus intensity. Higher correlations were found between the number of spikes and stimulus intensity. Measures of Signal Detection Theory indicated that the single unit discharges discriminated stimulus intensities better than the subjects' ratings. These findings underline the importance of temporal summation in the processing of C-fibre input with a considerable loss of information in the nociceptive system.     

Reaction times to painless and painful CO2 and argon laser stimulation

Summary The introduction of lasers in pain research has made it possible to activate the nociceptive system without activating mechanosensitive afferents. In the present study the reaction times to painless and painful laser stimuli were studied to investigate if the reaction time to experimental pain is reproduceable. CO₂ and argon lasers were used for stimulation, and the influence of stimulus (intensity and duration) and skin parameters (temperature, thickness, and reflectance) on reaction time were investigated. When these parameters were controlled the reaction times to painful CO₂ and argon laser stimulation were within the same range (350–450 ms), and the intra-individual variability minimal (6.9%). The reaction time was used to estimate peripheral conduction velocity (10 m · s^–1) for the activated fibre population when distinct pain was perceived. Determination of reaction times to non-painful and painful stimuli may be suitable ways to assess the functioning of thermal and nociceptive pathways.     

Prevention of operation wound sepsis by CO2 laser radiation: Experimental study in vivo

Research Institute of Laser Surgery, Ministry of Health of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR D. S. Sarkisov). Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 109, No. 5, pp. 456–457, May, 1990.     

CO2 responsivity in the mouse measured by rebreathing

We have modified the rebreathing method to study CO₂ responsivity in very small mammals. Tidal volume (V _T) and frequency (f) of pentobarbital-anesthetized mice were measured during rebreathing from a closed circuit, primed with 95% O₂, 5% CO₂, through which the gas was constantly circulated at 0.5 l·min^–1. The circuit consisted of T-tube from a plethysmograph, Tygon tubing with compliant element, CO₂ analyzer and pump, in series. CircuitPCO₂ (PctCO₂), which was recorded continuously during spontaneous breathing, rapidly equilibrated with end-tidalPCO₂. CO₂ response curves were constructed from extrapolated minute ventilation ( ),V _T,f and parameters of breath-to-breath timing, respectively, onPctCO₂. Analyses of slopes of the response curves, change from onset of rebreathing to peak response, andPctCO₂ at which the response peaked revealed that CO₂ stimulates by increasingf andV _T and that this is effected by facilitation of central inspiratory-expiratory phase switching and inspiratory drive mechanisms. However, the stimulatory effect of CO₂ on phase switching was not sustained, with maximal effect occurring before peak . The advantages and facility of the modified rebreathing method make it suitable for studies of other small mammals, including neonates.     

A new type of CO2 laser avoids power density loss due to absorption and the blooming effect by the CO2 gas environment

The aim of this study was to compare the acute tissue effectsof a standard CO₂ laser (Ultrapulse 5000) with a new design(Ultrapulse 5000L) that utilizes a different carbon isotope(C₁₃) in the rat uterine horn model. Following laparotomy, measuredlaser injuries were effected with the Ultrapulse 5000 or Ultrapulse5000L lasers via a laparoscope using CO₂or air for insufflation.Serial sections of the lesions were, thereafter, obtained toevaluate depth and width of total injury, width of defect andthermal damage zone. When CO₂ was used as the insufflating gas,Ultrapulse 5000L laser was associated with significantly deeperlesions compared to the Ultrapulse 5000 system for the two testedpulsed energy levels (P < 0.0001). The width of total injuryand thermal damage zone were significantly less with the formerlaser compared to the latter. The width of the defect was, however,significantly larger with the Ultrapulse 5000L laser for the200 millijoule pulsed energy level, whereas it was comparablefor the 75 millijoule level. When air was used as the insufflationgas, all four parameters of tissue injury were comparable betweenthe two types of laser (P > 0.05). The adverse effects onthe CO₂ laser beam and the resultant altered tissue effectsthat occur in a regular CO₂ environment are avoided by the useof the Ultrapulse 5000L or an air environment.     

Cerebral columnar organization of the first nociceptive component induced by CO2 laser on the tail of the rat

The somatotopic map of the first nociceptive component in the primary somatosensory cortex (S1) is still unclear. In this study, a CO(2) laser was applied to the tail of the rat to induce nociception without the interference from large myelinated (A(beta)) fibers. Thus, only noxious fibers could be activated. Two-dimensional current-source-density analysis was used to analyze the evoked field potentials. Using this method, the nociceptive responses of A(delta)-fibers in S1 were verified, and the somatotopic map of the first nociceptive component in S1 was identified. We found that whether light touch or laser-induced nociception was applied to the tail of the rat, the responsive topography in S1 was consistent. Discrimination of these two modalities was achieved vertically in the same column; the deeper layer represented the nociceptive response while the superficial layer encoded the response to light touch. This is quite different from that of a primate brain.     

Hyperpnoea and CO2 sensitivity of the respiratory centres during exercise

Summary The aim of this study was to specify whether exercise hyperpnoea was related to the CO₂ sensitivity of the respiratory centres measured during steady-state exercise of mild intensity. Thus, ventilation , breathing pattern [tidal volume (V _T), respiratory frequency (f), inspiratory time (T _I), total time of the respiratory cycle (T _TOT),V _T/T _I,T _I/T _TOT] and CO₂ sensitivity of the respiratory centres determined by the rebreathing method were measured at rest (SCO_{2 re}) and during steady-state exercise (SCO_{2 ex}) of mild intensity [CO₂ output =20 ml·kg⁻¹·min⁻¹] in 11 sedentary male subjects (aged 20–34 years). The results showed that SCO_{2 re} and SCO_{2 ex} were not significantly different. During exercise, there was no correlation between and SCO_{2 ex} and, for the same , all subjects had very close values normalized for body mass (bm), regardless of their SCO_{2 ex} ( =1.44 l·min⁻¹·kg⁻¹ SD 0.10). A highly significant positive correlation between SCO_{2 ex} andV _T (normalised for bm) (r=0.80,P<0.01),T _I (r=0.77,P<0.01) andT _TOT (r=0.77,P<0.01) existed, as well as a highly significant negative correlation between SCO_{2 ex} and (normalised for bm^−0.25) (r=−0.73,P<0.01). We conclude that the hyperpnoea during steady-state exercise of mild intensity is not related to the SCO_{2 ex}. The relationship between breathing pattern and SCO_{2 ex} suggests that the breathing pattern could influence the determination of the SCO_{2 ex}. This finding needs further investigation.     

CO2 rebreathing model in COPD: blood-to-gas equilibration

Rebreathing in a closed system can be used to estimate mixed venous and cardiac output, but these estimates are affected by heterogeneity. The purpose of this study was to validate a mathematical model of CO₂ exchange during CO₂ rebreathing in 29 patients with chronic obstructive pulmonary disease (COPD), with baseline arterial ranging from 28 to 60 mmHg. Rebreathing increased end-tidal by 20 mmHg over 2.2 min. This model employed baseline values for inspired (bag) estimated distribution of ventilation and blood flow in one high and one low compartment, the ventilation increase and conservation of mass equations to simulate time courses of and Measured and during rebreathing differed by an average (SEM) of 1.4 (0.4) mmHg from simulated values. By end of rebreathing, predicted was lower than measured and predicted indicating gas to blood CO₂ flux. Estimates of the ventilatory response to CO₂, quantified as the slope (S) of the ventilation increase versus were inversely related to gas-to-blood disequilibria due to heterogeneity and buffer capacity (BC), but not airflow limitation. S may be corrected for these artifacts to restore S as a more valid noninvasive index of central CO₂ responsiveness. We conclude that a rebreathing model incorporating baseline heterogeneity and BC can simulate gas and blood in patients with COPD, where variations are large and variable.Laboratory of origin: These experiments were performed at the Lovelace Medical Foundation and at New Mexico Resonance in Albuquerque NM.     

Ventilatory CO2 response in endurance-trained rats

Summary A CO₂ rebreathing technique was used to assess possible changes in the ventilatory response to CO₂ in rats following a 14-week swim training program. Over the final 9 weeks, the rats swam 1 h per day with a weight of 2.5% of the body weight attached to the tail. Ventilation was measured by a barometric method in awake, restrained rats in a total body plethysmograph at CO₂ concentrations of 0, 2, 4, 6, and 8%, with an initial O₂ concentration of approximately 100%. Ventilation increased in the trained rats with increasing CO₂ from 775 ml·min^–1·kg^–1 at 0% CO₂ to 1,387 ml·min^–1·kg^–1 at 8% CO₂. This increase was a consequence of a 34% increase in tidal volume and a 32% increase in breathing frequency. In comparison with a group of sedentary control rats, there was a significantly higher ventilation and tidal volume at 0% CO₂; however, this difference disappeared with increasing levels of CO₂. A significantly lower resting heart rate was observed in the exercised (296±44 beats·min^–1, mean±SD) compared to the sedentary control rats (380±42). It was concluded that, while the normal training response of resting bradycardia was observed following this duration and intensity of training, endurance swimming had no significant effect on the ventilatory response to CO₂ in the rat.This research was funded in part by grants from the University of Waterloo Research Foundation, the Ontario Heart Foundation, and the Medical Research Council of Canada     

Modulation of heat evoked nociceptive withdrawal reflexes by painful intramuscular conditioning stimulation

Convergence between cutaneous heat nociceptors and muscles afferents was investigated by applying a phasic, conditioning electrical stimulus to the tibialis anterior muscle (a train of five 1 ms pulses over 21 ms) at varying time intervals relative to a thermal test stimulus used for evoking the withdrawal reflex in humans. The 200 ms thermal stimulus was applied on the dorsum of the foot at an intensity of two times the pain threshold. The conditioning electrical stimulus was applied at an intensity of two times the pain threshold via a set of intramuscular needle electrodes. The conditioning-test interval was varied between –400 ms and 8,000 ms at 17 different intervals. The mean reflex onset latency of reflexes evoked by thermal stimuli alone was 354 ± 9 ms. A facilitation of the reflex was seen when the conditioning stimulus was applied 275 ms (174 ± 30% compared to control) and 300 ms (162 ± 32% compared to control) after the test stimulus onset indicating sensory convergence between muscle afferents (group I–III) and cutaneous Aδ heat nociceptors arriving simultaneously at the spinal cord.     

A Mathematical Model to Predict CO2 Removal in Hollow Fiber Membrane Oxygenators

A mathematical model has been developed to predict CO₂ removal in hollow fiber membrane oxygenators. The model is analogous to one developed previously for predicting O₂ transfer. A mass transfer correlation was determined in water for O₂ and CO₂ exchange and collapsed onto one universal curve. The correlation was used to predict CO₂ removal in blood by incorporating a ‘facilitated diffusivity’ to account for the transport of CO₂ present as bicarbonate. The diffusion of bicarbonate greatly increased the ability of the oxygenator to remove CO₂ in blood compared to water. A fiber bundle module was fabricated to test the model predictions. The fiber bundle had a length of 13 cm and a bundle thickness of 0.2 cm. The module was tested in bovine blood at flowrates of 0.75, 1.5, and 2.2 L/min and CO₂ removal rate predictions were within 9% of experimental measurements at all flowrates. The O₂ transfer rate predictions were within 10% of experimental measurements. A second module was manufactured with a bundle of length 4 cm and thickness of 1 cm. The CO₂ removal predictions were within the standard deviation of the experimental measurements.     

Massenspektrometrische Bestimmung des O2- und CO2-Gehaltes von Blut

Zusammenfassung CO₂ und O₂ werden durch einen Trägergasstrom (N₂ reinst) aus dem Blut extrahiert und die Konzentration dieser Gase im konstanten Gasstrom fortlaufend massenspektrometrisch gemessen. Das Integral der Konzentration über der Zeit ist proportional der ausgetretenen Gasmenge. Die Eichung erfolgt durch Eingabe abgemessener Volumina von O₂ und CO₂ in den Trägergasstrom. Analysendauer: 2 min.     

Maximal breath-holding time and immediate tissue CO2 storage capacity during head-out immersion in humans

This study tested three possible mechanisms that could explain the prolonged breath-holds (BH) previously observed in humans during submersion in 35°C (thermoneutral) water, including a reduced metabolism, a decreased CO₂ sensitivity, and an increased CO₂ storage capacity. During immersed BH (n = 13), maximal BH time was prolonged by 20.3% (P < 0.05), the rate of rise of end tidal partial pressure of carbon dioxide (P _ETCO₂) was slower (P < 0.05) by 31 % (compatible with increased CO₂ storage capacity), but the breaking-pointP _ETCO₂ (CO₂ sensitivity) and the rate of decrease of end tidal partial pressure of oxygen (metabolism) were unchanged. During air breathing (n = 5), immersion resulted in a significant decrease in tidal volume (11%), but did not affect O₂ uptake, CO₂ elimination , or respiratory exchange ratio (R). During a 4-min CO₂-rebreathing (n = 9), the slope of the hypercapnic ventilatory response curve (CO₂ sensitivity index) was unchanged by immersion, but the significantly decreased ,R, and rate of rise inPETCO₂ during immersed rebreathing indicated an increase in the acute CO₂ storage capacity (SC). The estimated SC (n = 9), based on an assumed cellular respiratory quotient of 0.8, were 0.52 (SEM 0.03) ml · kg⁻¹ · mmHg⁻¹ for control and 0.66 (SEM 0.04) ml · kg⁻¹ · mmHg⁻¹ for immersion. A proposed mechanism for the increased SC during immersed BH and during immersed rebreathing is that immersion accelerated CO₂ redistribution in the body by increasing perfusion to some low-perfused, low-metabolism, and high-capacity tissues, such as resting skeletal muscle. The increased SC during immersion, however, did not correlate with the prolonged BH duration (n = 9,P > 0.05). The mechanism of the latter remains unclear.     

Comparison of arterial,end-tidal and transcutaneous PCO2 during moderate exercise and external C02 loading in humans

Summary Static relationships between arterial, transcutaneous[/p] and end-tidal PCO₂ (P _aCO₂, P _tc CO ₂, P _etCO₂) as well as the dynamic relationship between P _etCO₂ and P _tcCO₂ were studied during moderate bicycle ergometer exercise with and without external C0₂ loading. The exercise pattern consisted of 5-min intervals of constant power at 40 W and 100 W and 900 s of randomised changes between these two power levels. The external CO₂ loading was achieved by means of controlled variations of inspiratory gas compositions aimed at a constant P _etCO₂ of 6.5 kPa (49 mm Hg). The P_etO2 was regulated at 17.3 kPa (130 mm Hg). Under steady-state conditions all PCO₂ parameters showed close linear relationships. P _aCO₂/P _tcCO₂ was near to identity while the P _etCO₂ systematically overestimated changes in P _aCO₂. No relationship showed a significant influence of the exercise intensity. Transients of P _tcCO₂ are considerably slower than P _etCO₂ transients. The dynamic relationship between both parameters was found to be independent of whether internal or external C0₂ loadings were applied. It is concluded that the combination of P _etCO₂ and P _tcCO₂ measurements allows an improved non-invasive assessment of P _aCO₂. While P _etC0₂ better reflects the transients, P _tcCO₂ can be employed to determine slow changes of the absolute P _aCO₂.     

Three successive steady-state CO2-response curves

Three successive steady-state CO₂-response curves, with 10-minute intervals, were taken in seven healthy subjects at rest in normoxia. No systematic difference in the slopes between the three curves could be found. The results suggest that a previous steady-state CO₂-response curve does not change the sensitivity of the ventilatory controlling system for CO₂.     

Ventilatory response to oscillating and non-oscillatingPa CO 2 in the anesthetized cat

Summary In 11 adult cats, lightly anesthetized with chloralose-urethane, blood from both common carotid arteries was led into a plastic chamber of 15–20 ml and returned to the carotids at a point 1.5 cm more cranial. By doing so arterial blood was assumed to pool within the chamber and lose itsP _{CO 2} oscillations which are normally known to exist as a result of the respiratory cycle. In control periods blood bypassed the chamber, thus maintaining respiratoryP _{CO 2} oscillations. Spontaneous ventilation was measured spirometrically. The animals were breathing pure O₂.Results. 1. When the sinus (carotid) nerves were intact or sectioned there was no significant difference in ventilation before or after switching from non-oscillating to oscillatingPa _{CO 2}. 2. When the vertebral arteries were ligated a drop in ventilation occurred after turning to oscillatingPa _{CO 2} which was followed by a slight rise above control values after 30–50 sec. This phenomenon was independent of sinus nerve integrity. Thus in hyperoxie condition the smallPa _{CO 2} oscillations known to occur in phase with respiration do not seem to provide a respiratory stimulus to resting ventilation above that generated by the mean level ofPa _{CO 2}. The ventilatory depression after vertebral artery ligation must at this time remain unexplained.