Reliability of Cutaneous Oxygen Measurement by Skin Sensors with Large-Size Cathodes

The oxygen partial pressure may be measured cutaneously by directly heated P_o2 sènsors attached to the surface of the skin. The use of a large-size cathode (diameter 4 mm) allows one to obtain an average P_o2 value over a sufficiently large skin area.
The permeability of the membrane for oxygen has to be kept low to prevent a disturbance of the oxygen profile in the cutaneous tissue as a result of the oxygen consumption of the sensor. When using a 6 μm Mylar membrane, the current can be limited by the diffusion of oxygen through the membrane and is a measure of the arterialized cutaneous P_o2.
One effect of using a membrane of low permeability is that the response time of the sensor is long (± 90% = ca 45 sec). The reliability of correctly reproducing cP_o2 variations by sensors having different response times may be evaluated by determining the transfer function of the membrane which allows the calculation of the frequency characteristics for various membranes. The cutaneous tissue layer also acts as a filter for rapid P_o2 fluctuations. The characteristic of this filter is essentially similar to that of a 'slow' membrane such as Mylar 6 μm. The information gained by using a 'rapid' membrane such as Teflon 13 μm is negligible.
In 490 comparative measurements in newborns performed with sensors heated to 44C, the correlation between arterial P_o2 and cutaneously measured P_o2 is significant (correlation coefficient = 0.934) and the regression line does not deviate significantly from the identity line.     

Dermal Heat Transport Analysis for Transcutaneous O2 Measurement

Heat from a transcutaneous oxygen electrode is transmitted locally to the blood beneath it causing a shift in the HbO₂ dissociation curve. This increases the local PO₂, and allows a measurable PO₂, at the skin surface. The temperature effect on the HbO₂, curve must be accounted for in in vivo calibration of Ptco₂, data. To do this, the capillary blood temperature beneath the electrode must be known. A heat balance is written around the capillary blood with heat being conducted in from the electrode and carried out by two means: conduction to deep tissue; and transport away by the flowing capillary blood. The following equation is the steady state solution of the heat transport problem:
T₈ = ±
where Z = ± = 0.17
T₈, = capillary blood temperature
T₁ = electrode temperature
T_o = body temperature
ρ = blood density
P = cutaneous perfusion
δ = dermal capillary depth
k = thermal conductivity of skin
C± = heat capacity of blood
This solution shows the capillary blood temperature may be calculated if the T₁ and T_o are measured and the physiologic constants in 2 are known. 2 is a dimensionless heat transport number which represents the relative importance of perfusion to conduction effects on the deterring T₈, and may be used as a data correlating parameter. Z = 0.17 is obtained using literature values for the physiological constants. This analysis used in conjunction with a mass transport analysis for oxygen will produce a theoretically based correlation scheme for in vivo calibration of heated transcutaneous oxygen electrodes.     

*Cardiovascular Research Institute and Department of Anesthesia, University of California School of Medicine, San Francisco, CA 94143

Transcutaneous P_co2 electrodes have been constructed and evaluated on adults and children. Glass pH and silver reference electrodes were used at 44–45C, with either circulating water and a copper jacket, or with internal electrical heating. The skin surface P_co2 at 44C is about 1.33 times Pa_co2 plus 3 mmHg when measured with electrodes calibrated in gas at 44C. Three temperature effects combine in this ratio: Heating raises blood Pco2 4.5%/C, skin metabolism adds about 3 mmHg, and the cooling of the electrode active surface by skin increases electrode reading. Response time to step changes of Pa_co2 was about 3 min to 63%, of which 1.2 min was sensor delay, the remainder skin C0₂ washout. It was found important to use ethylene glycol-water mixtures rather than water for electrolyte to avoid bubble generation and drift. Heat transfer through the pH glass electrode has been increased by enlarging the internal silver electrode to virtually fill the entire glass electrode. Time required for initial vasodilation and stabilization is similar to that of tcP_o2 electrodes, and accuracy of determination of Pa_co2 appears to be better than ± 2 mmHg.     

Transcutaneous Blood Gas Measurements Using a Mass Spectrometer

We use a Perkin Elmer MGA 1100 mass spectrometer modified for blood gas tension measurements to study transcutaneous measurements of oxygen, carbon dioxide, nitrogen and helium in normal subjects. We use an aluminum sampling chamber heated to 42–44C and connected to the mass spectrometer by about 2 m of stainless steel tubing. The sampling area of 5 cm² is covered with a polytrifluoro-chloroethylene membrane 18 μn thick (Allied Chemical Co., Aclar 33C). The membrane is supported by a sintered stainless steel disc with a thermistor incorporated for measurement of "membrane" temperature. The chamber is heated with a printed circuit heater (Minco) and is temperature regulated by a servo circuit.
We have used the system to measure O₂, CO₂, N₂ and He via the heated skin in four normal subjects, breathing air and then 100% oxygen. We also observed the response to a single breath of helium. Helium appears at the skin within 10–15 sec. The time constant of its disappearance is about 70 sec. The average uncorrected gas tensions which we obtained breathing air were 11.2 kPa for oxygen, 5.1 kPa for carbon dioxide and 67.1 kPa for nitrogen. The corresponding values breathing oxygen were 41.1 kPa for oxygen, 4.4 kPa for carbon dioxide and 13.1 kPa for nitrogen.     

Desflurane increases brain tissue oxygenation and pH

Background Desflurane anesthesia can produce cerebral metabolic depression and increase cerebral blood flow. We evaluated the effect of desflurane on brain tissue oxygen pressure (PO₂), carbon dioxide pressure (PCO₂) and pH during neurosurgery.
Methods: Following a craniotomy, the dura was opened and a Paratrend 7 sensor, which measures PO₂, PCO₂, pH and temperature, was inserted into brain tissue. In 6 control patients in group 1, anesthesia was maintained constant with 3% end-tidal desflurane over 60 min, including a 30-min stabilization period. In group 2, 9 patients were ventilated with 3% desflurane under baseline conditions. After a 30-min stabilization period, baseline tissue gases and pH were measured and end-tidal desflurane was increased to 6% and then 9% for 15-min intervals. Mean arterial pressure (MAP) was maintained with intravenous phen-ylephrine.
Results: Under baseline conditions, cardiovascular and brain tissue measures were similar between the 2 groups. Increasing end-tidal desflurane from 3% to 9% produced burst-suppression EEG in all patients and significantly increased tissue PO₂ and pH and decreased PCO₂. No parameters changed significantly in the control group during steady-state anesthesia.
Conclusion: These results show that 9% desflurane can improve brain tissue metabolic status before temporary brain artery occlusion if cerebral perfusion pressure is maintained. This may be particularly important in patients with symptoms of ischemia before surgery.     

In Vivo vs. In Vitro Response Time of Trancutaneous Po2 Electrodes A comparison of four devices in newborn infants

Four devices for transcutaneous P_o2 (tcP_o2) monitoring have been applied simultaneously in 16 infants. Both during a maximal change in Pa_o2 and during physiological P_o2 variations, the in vivo response time of the electrodes did not show the differences observed in vitro.
We compared A, a prototype of the electrode by Huch, Lübbers and Huch (25 μm Teflon membrane); B, the commercial version of A by Hellige-Draeger (25 μm Teflon); C, the Radiometer TCM I oxygen monitor (25 μm polypropylene); and D, the Roche macrocathode electrode (6 μm Mylar), at 44C.
In vitro the 50% response times were 2.9 ( A ), 4.4 ( B ), 3.7 ( C ), and 7.4 ( D ) sec. The rates of tcP_o2 changes at the midpoint of the response curves were 3.8 ( A ), 2.0 ( B ), 3.0 ( C ), and 1.7 ( D ) kPa/sec.
In vivo during a sudden change from hyperoxaemia (Fi_o2 1.0) to normoxaemia the respective rates were 0.6 ( A ), 0.8 ( B ), 1.1 ( C ) and 1.0 ( D ) kPa/sec. The in vivo 50% response times were 53.3 ( A ), 51.1 ( B ), 46.2 ( C ), and 45.3 ( D ) sec. The lag time between Pa_o2 and tcP_o2 was about one third of this overall response time.
The response to more physiological variations of Pa_o2 (periodic breathing) was not different among the tested electrodes in terms of damping and of delay of the tcP_o2 deflections. In a steady state the correlation of tcP_o2 44C vs Pa_o2 was close ( r = 0.98) with all devices up to 6.1 kPa (456 torr).     

Use of the Combitube for airway maintenance during percutaneous dilatational tracheostomy

The Combitube airway allows short-term ventilation during cardiopulmonary resuscitation and can be useful in the management of the difficult airway. In a prospective observational study we assessed its use during percutaneous dilatational tracheostomy (PDT). Twenty-one intensive care patients scheduled for elective PDT had their tracheal tube replaced by a Combitube airway retaining the same ventilator settings. Arterial blood gases, airway pressures, SpO₂ and end-tidal CO₂ were measured as were the transmural pressures exerted by the Combitube cuffs. Combitube placement was successful in 20 of 21 patients although adequate ventilation was possible in only 17 (85%). There was no significant change in P a O ₂, S p O ₂, end-tidal CO₂, P a CO ₂ or mean airway pressure during Combitube ventilation. A high mean (SD) transmural pressure of 14.7 (5) kPa was exerted by the distal cuff. The Combitube provided a satisfactory alternative airway to the tracheal tube during performance of PDT in 85% of our patients. Potential problems associated with its use in intensive care patients are outlined.     

Haemodynamics during inhalation of a 50% nitrous-oxide-in-oxygen mixture with and without hypovolaemia

Background: Inhalation of a gas mixture containing 50% nitrous oxide in oxygen (N₂O/O₂) is widely used for pain relief in emergency situations, which may also be associated with blood loss. The aim of this study was to evaluate the haemodynamic effects of this gas mixture in normo- and hypovolaemic subjects.
Methods: Six healthy males were studied during inhalation of N₂O/O₂ before and after withdrawal of 900 ml of blood. On each occasion, we measured systemic and pulmonary arterial pressures, cardiac output, blood gases, extravascular lung water, and the blood flow and oxygen consumption in the whole body, liver and kidneys.
Results: Inhalation of N₂O/O₂ reduced the stroke volume and increased peripheral resistance. Oxygen uptake decreased in the liver (-30%) and in the whole body (-23%). Blood withdrawal reduced the pulmonary arterial and central venous pressures (-30 to -50%) and further decreased stroke volume and the blood flows to the liver and the kidney (-15%). The extravascular lung water tended to increase both during inhalation of N₂O/O₂ and during hypovolaemia.
Conclusion: N₂O/O₂ aggravated the hypokinetic circulation induced by hypovolaemia. However, the oxygen consumption decreased only during inhalation of N₂O/O₂. This opens up the possibility that the cardiodepression associated with N₂O/O₂ is caused by a change in metabolic demands.     

Pulmonary inflammatory mediators after sevoflurane and thiopentone anaesthesia in pigs

Background:  Volatile anaesthetics have been shown to affect the release of pulmonary inflammatory mediators and exacerbate pulmonary injury after experimental aspiration. Thus, in theory, volatile anaesthetics may worsen inflammatory pulmonary injury and disease. We have previously described that no significant changes in alveolar ultrastructure are seen after sevoflurane anaesthesia. However, this does not exclude any possible physiological alterations. The aim of our study was to evaluate pulmonary inflammatory mediators in bronchoalveolar lavage (BAL) after sevoflurane and thiopentone anaesthesia in pigs with intact lungs.
Methods:  Sixteen pigs were randomly selected to receive either a continuous thiopentone infusion (control group, n = 8) or sevoflurane (n = 8) at 4.0% inspiratory concentration (1.5 MAC) in air for 6 h. Bronchoalveolar lavage samples were collected at the end of the study to determine pulmonary inflammatory markers.
Results:  Compared with thiopentone anaesthesia, significant increases in BAL leukotriene C₄ (LTC₄), NO₃-, and NO₂- levels were observed after sevoflurane anaesthesia. In addition, there was a significant decrease in total blood leukocyte count in sevoflurane-treated animals.
Conclusion:  We conclude that sevoflurane increases pulmonary LTC₄, NO₃-, and NO₂- production in pigs, indicating an inflammatory response.     

From in vitro to in vivo monitoring

In vitro monitoring is inherently invasive with discrete measurements on blood samples and the results are often delayed an hour or more when the analyses are performed in the central laboratory. The delay may be greatly reduced if the analyses are performed near the patient. In vivo monitoring may be non-invasive and may provide continuous real-time data but the accuracy usually does not match that of in vitro measurements. In vivo monitoring therefore finds its application in the detection of trends of change, and it is needed only for quantities that change rapidly and unpredictably and where a suitable therapeutic action is available. In critically ill patients, this applies to the arterial p O₂, p CO₂, and pH, and the mixed venous p O₂. Ideal in vivo monitoring techniques are not available for all these quantities. In the newborn, the arterial p O₂ may be monitored with a transcutaneous p O₂ electrode. In the adult, the arterial p O₂ may be monitored indirectly by monitoring the arterial oxygen saturation with a pulse oximeter and the mixed venous p O₂ by monitoring the mixed venous oxygen saturation with a catheter tip sensor. The arterial p CO₂ may be monitored with a transcutaneous p CO₂ electrode or by capnography, i. e., by monitoring the end-expiratory p CO₂. Other in vivo monitoring techniques such as gastric tonometry for the gastric mucosal pH and thoracic impedance measurement have found some routine application, whereas near-infrared spectrometry for oxy- and deoxyhaemoglobin in the brain, and magnetic resonance spectroscopy for tissue ATP are at the stage of research and development.     

Intraarterial Perfusion of the Hindlimb with Pyridoxalated Hemoglobin Polyoxyethylene Conjugate Solution in Anesthetized Dogs

Abstract: To evaluate the potential clinical usefulness of a modified hemoglobin, pyridoxalated hemoglobin polyoxyethylene conjugate (PHP), the hindlimb vascular bed was perfused with PHP solution while monitoring tissue oxygen tension (Pto₂) in anesthetized dogs. The hindlimb region was perfused through the external iliac artery with a roller pump at a varying perfusion rate. Pto₂ was measured using a Po₂-monitoring probe inserted into the gra-cial muscle. After surgical preparation for perfusion, the iliac arterial flow rate was 19.9 ± 5.6 ml/min, and baseline Pto₂ was 38.4 ±1.3 mm Hg. Perfusion with autologous arterial blood with the pump increased Pto₂ and perfusion pressure (PP) in a perfusion rate-dependent manner. Perfusion with PHP solution at 20 ml/min decreased Pto₂ from the initial baseline level, but an increase in the flow rate to 40–55 ml/min restored or induced an elevation of Pto₂. Results demonstrated that PHP solution can deliver oxygen to local tissue and maintain tissue oxygen tension at the same level as autologous arterial blood at a high enough flow rate.     

Determination of Skin Blood Flow by 133Xe Washout and by Heat Flux from a Heated tc-Po2 Electrode

¹³³Xe washout measurements were used to determine cutaneous and subcutaneous blood flow beneath a specially designed double-thermostated tc-Po₂ electrode. The skin blood flow was determined using thermal methods based on reduced heat dissipation during blood flow cessation. A total of 20 measurements were performed on two healthy volunteers, using the volar side of the right forearm as the experimental area. Cutaneous as well as subcutaneous blood flow increased with increasing electrode temperature. The cutaneous blood flow increased from 12.3 ± 1.3 ml (100 g)^-1-min^-1 (37C) to 49.1 ± 5.4 ml (100 g)^-1.min^-1 (45C) and the subcutaneous values from 20.9 ± 0.2 ml (100 g)^-1 -min^-1 to 57.3 ± 0.5 ml (100 g)^-1 -min^-1. Preheating of the measuring area or injection of papaverine as blood flow accelerator did not increase the maximum blood flow values. A considerable inter-individual difference between cutaneous and subcutaneous blood flow was observed, but in spite of that a good overall correlation between the ¹³³Xe washout measurements and the two thermal flow measurements was found (r = 0.932 and 0.945, respectively). It is concluded that in some cases, but not always, measurements of tc-Po₂ at electrode temperatures of 45C take place on a maximally perfused skin and that it is possible to determine skin blood flow by means of determinations of the heat dissipated from the tc-Po2 electrode to the underlying skin.     

CD4+ and CD8+ T cell subset distribution in the blood of small-bowel-grafted rats: modification during graft-versus-host disease

Abstract We studied the modifications of blood T cell distribution following small-bowel allografting in rats under different experimental conditions. Group 1: ACI (RT1^a) rats were used as small-bowel donors for ACI × Wistar (RT1^y) F₁, hybrid rats (WAF₁) in which graft-versus- host disease (GVHD) developed. Group 2: WAF₁ rats were used as small bowel donors to ACI rats which developed rejection. Group 3: WAF₁ rats received small bowel from ACI rats hyperimmunized for 10 days (by grafting them with WAF₁ skin) and GVHD developed. Group 4: Wistar rats received small bowel from ACI rats hyperimmunized for 10 days (by Wistar skin) and bidirectional GVHD and rejection were assured. A second set of the same groups which were continuously administered with cyclosporin (15 mg/kg per day s.c. for 15 consecutive days) was also studied. Recipient peripheral blood lymphocytes, obtained at 7 and 15 days following small-bowel transplantation, were stained with monoclonal antibodies anti-rat CD4 and CD8 and then analyzed in an automated flow cytometer. A significant major reduction of CD4⁺/CD8⁺ T cell ratios was shown in rats that developed simultaneous GVHD and rejection with respect to ungrafted rats.     

Continuous low-flow tracheal gas insufflation during partial liquid ventilation in rabbits

Background: Both partial liquid ventilation (PLV) and tracheal gas insufflation are novel techniques for mechanical ventilation. In this study we examined whether PLV superimposed by continuous low-flow tracheal gas insufflation (TGI) offers any advantage to the blood gases and lung mechanics in normal-lung rabbits compared to the use of PLV only.
Methods: Eighteen anesthetized, paralyzed and mechanically ventilated rabbits were used. After obtaining a baseline PaCO₂value between 29 and 39 mmHg (3.9 and 5.2 kPa), the animals were assigned to three equal groups according to the ventilation they received - A group: PLV superimposed by TGI; B group: PLV only; and C group: continuous mandatory ventilation (CMV) superimposed by TGI. Serial arterial blood gases, pH and lung mechanics were measured.
Results: The animals in each group were hemodynamically stable. In the case of the A group, PaO₂ continuously increased, and PaCO₂ stabilized around 40.8±5.5 mmHg (5.4±0.7 kPa, mean±SD, NS). In the B group, the tendency for PaO₂ to increase was not as definite; PaCO₂ continuously increased from 35.2±2.3 mmHg (4.7±0.3 kPa) to 56.3±12.7 mmHg (7.5±1.7 kPa, P < 0.05) at the end of the experiment. In the C group, PaO₂ and PaCO₂ were stable during the observation period. The superimposition of TGI on PLV did not decrease the airway pressures compared to PLV alone.
Conclusion: In summary, continuous low-flow TGI superimposed on PLV can decrease and stabilize the PaCO₂ elevation caused by the initiation of PLV.     

Differential effects of dobutamine, dopamine, and noradrenaline on splanchnic haemodynamics and oxygenation in the pig

Supranormal oxygen (O₂) transport may benefit critically ill patients. Catecholamines are clinically employed for this purpose. However, their effects on splanchnic haemodynamics and oxygenation are not well defined. The effects of dobutamine (DOBU), dopamine (DOPA), and noradrenaline (NA) on splanchnic blood flows (electromagnetic flow probes), O₂ deliveries and uptakes (catheterisation of portal and hepatic veins) were studied in nine anaesthetised (ketamine/flunitrazepam), ventilated, paralysed, and laparotomised pigs. All three catecholamines (DOPA at 15 μg·kg^-1 · min^-1, DOBU at 13 μg · kg^-1 · min^-1, NA at 0.4 μg · kg^-1 · min^-1) significantly ( P <0.05) increased cardiac output and systemic O₂ delivery. Only DOPA increased small intestinal and total hepatic blood flows, and O₂ deliveries, and decreased O₂ extractions. The same parameters did not change during DOBU. During NA, total hepatic blood flow and O₂ delivery decreased, and hepatic O₂ extraction increased. During all three catecholamines, small intestinal and total hepatic O₂ uptakes did not change significantly. Whereas hepatic arterial blood flow decreased during both DOPA and NE, portal venous flow increased during DOPA. These data suggest that in the experimental model used splanchnic O₂ supply and O₂ reserve capacity appear improved by DOPA, unaffected by DOBU, and impaired by NA.     

A Transcutaneous Po2 Electrode Incorporating a Thermal Clearance Local Blood Flow Sensor

Several possible methods for estimating and recording skin blood flow by thermal clearance are presented. The method chosen for trial with an O₂ electrode was to thermoregulate an annular anode which covered the cathode, surrounding it like a heat shell, and to measure the cooling of the cathode by blood flow, by implanting a thermistor near the surface of the cathode. This device is far less affected by ambient temperature than is simple measurement of heating power in an uninsulated tcP_o2 electrode.     

The effects of multiple small doses of exogenous surfactant on experimental respiratory failure induced by lung lavage in rats

Aim: To test the effect on pulmonary gas exchange and mechanics of multiple small doses of exogenous surfactant as an alternative to bolus delivery in experimental respiratory failure induced by lung lavage.
Methods: After anesthesia, tracheostomy and constant volume ventilation, respiratory failure was induced by lung lavage in 20 rats. Animals were randomly assigned to an untreated control group or two experimental groups. Equal total doses of modified porcine surfactant (200 mg ·kg^-1 body weight,) were given by tracheal instillation, either as a single bolus or in four (50 mg·kg^-1 b.w.) fractional doses at 10-min intervals. Arterial pH and blood gases, and peak inspiratory pressure (PIP) were measured.
Results: After lavage, a rapid decrease in arterial pH and PaO₂, and an increase in PaCO₂ and PIP were observed in all animals. In both surfactant-treated groups, PaO₂ increased after surfactant instillation, and remained significantly higher than controls throughout the experiment. Arterial pH was significantly higher and PaCO₂ significantly lower only in the single bolus group. In the multiple dose group, these levels were similar to those of controls.
Conclusions: In surfactant-depleted rats with respiratory failure, instillation of four fractional surfactant doses did not result in the same enhancement on gas exchange and PIP, in the following 60 min, as same total dose given by a single bolus.     

Influence of age on circulation and arterial blood gases in man

Background. Modem data on the influence of age on hemodynamic and blood gas data in healthy subjects are sparse, especially in middle aged or older subjects. Most measurements have been done in patients during major surgery or in intensive care when the patients have one or more failing organ systems. This study reports on hemodynamics, blood gases and blood volume in healthy patients prior to anesthesia and elective surgery.
Methods. A total of 116 subjects (92 males, 24 females) were investigated prior to anesthesia and elective surgery. No one had received any premedication or was taking regular medication. All subjects were in good physical condition, except for their surgical disease, and clinical examination and history did not reveal any sign of cardiopulmonary disease. Measurements were made of systemic and pulmonary vascular pressures, cardiac output, arterial blood gases and blood volume by ¹³¹I-Albumin distribution.
Results. Cardiac output, stroke volume, and blood volume correlated to body surface. Relating these variables to body size eliminated almost all differences between the male and female groups. These variables, as well as both systemic and pulmonary artery systolic vascular pressures, were affected by increasing age. Pulmonary capillary wedge and right atrial pressures were not influenced by age. PaO₂ decreased with age from 14.0 kPa at 20 years to 11.3 kPa at 80, whereas PaCO₂ was unaltered. No effect of light smoking was found on pulmonary circulation or arterial blood gases. Significant correlations were found between blood volume on the one hand and body size and age on the other hand, but not in regard to sex.     

Pulmonary sympathetic denervation does not increase airway resistance in patients with chronic obstructive pulmonary disease (COPD)

Whether or not neural blockade of pulmonary sympathetic innervation is of relevance for airway resistance in patients with chronic obstructive pulmonary disease (COPD) is unknown. Accordingly we evaluated airway resistance during sympathetic blockade by high thoracic epidural anaesthesia in patients with COPD. Before and 45 min after thoracic epidural injection of bupivacaine 0.75% (6–8 ml; n=10) total respiratory resistance (oscillometry, R_os), vital capacity (VC), forced expiratory vital capacity in 1 s (FEV₁, [% VC]), functional residual capacity (FRC; helium dilution method), and arterial blood gases were measured. Three additional patients received bupivacaine intravenously (1.2 mg . min^-1 for 45 min), another three received saline epidurally. Sensory blockade covered segment C₅ through T₈. As an indicator of widespread sympathetic blockade including the lungs, skin temperature increased significantly on thumb and little toe. Despite pulmonary sympathetic denervation R_os, FEV₁, and FRC remained unchanged, while VC decreased slightly, probably due to intercostal muscle blockade. Blood gases remained constant. Neither intravenous bupivacaine nor epidural saline evoked directional changes. Since, in contrast to β-adre-noceptor blockade, pulmonary sympathetic denervation did not increase airway resistance in patients with COPD, neural sympathetic blockade seems to be of no relevance for airway resistance in these patients.     

Continuous Comparison of Transcutaneous and Arterial Oxygen Tension in Newborn Infants with Respiratory Illnesses

Transcutaneous oxygen tension (tcP_o2) measured by two skin electrodes of different design, and arterial oxygen tension (Pa_o2) measured by an intravascular oxygen electrode, were continuously compared for periods of 6–27 h in 45 newborn infants with respiratory illnesses. One skin electrode (Dräger) had three micro-cathodes surrounded by a heated ring-shaped anode and the other (Roche) a large heated cathode. The electrodes were calibrated in vitro; 44C was found to be a suitable electrode temperature for the estimation of Pa_o2.
tcP_o2 recorded by the electrode with the microcathodes estimated Pa_o2 reasonably accurately for 6 h without the necessity for re-siting. tcP_o2 recorded by the electrode with the large cathode gave a similar estimate of Pa_o2 for 3 h, but then tcP_o2 often fell relative to Pa_o2. This fall was probably caused by skin changes at the electrode site. Poor skin perfusion causing underestimation of Pa_o2 by tcP_o2 could not be identified by a number of methods tried.