Desaturation Curve Research Articles

Patterns of oxygenation during periodic breathing in preterm infants

The characteristics of the arterial oxygen saturation (Sao 2) signal during episodes of hypoxaemia (Sao 2 ≤ 80% for ≥ 4 s) associated with periodic and non-periodic apnoeic pauses were studied in 16 preterm infants with cyanotic episodes (patients), and 15 asymptomatic preterm infants (controls), matched on birthweight and gestational age. The patients showed a significantly higher percentage of apnoeic pauses followed by a hypoxaemic episode (25 vs. 6%, P < 0.01), and a two-fold increase in the slope of the desaturation curve (8.4 vs. 4.3% per s, P < 0.005) in periodic compared with non-periodic breathing. All other characteristics of oxygenation (baseline SaO2 before episodes of hypoxaemia, delay between onset of apnoeic pause and onset of desaturation, lowest Sao2 during episodes of hypoxaemia) were similar for periodic and non-periodic breathing patterns. Similar, but not significant, differences between isolated and periodic apnoeic pauses were also present in the controls. An analysis of episodes of bradycardia (≤ 100 beats per minute (bpm)) showed that out of 121 episodes in the patients 118 were accompanied by a fall in SaO 2 to ≤ 80%, and in the remaining three SaO 2 fell to 82%, 85% and 86%, respectively. Thus all episodes of bradycardia (≤ 100 bpm) were associated with a fall in SaO 2 detected by beat-to-beat pulse oximetry. Examination of hypoxaemic episodes and their relationship with bradycardia and with apnoeic pauses, periodic and non-periodic, may help the further understanding of the control of arterial oxygenation in preterm infants with cyanotic episodes.

Influence of Apnea Type and Sleep Stage on Nocturnal Postapneic Desaturation

We examined the influence of apnea type and sleep stage on the severity of apnea-induced desaturations in 32 patients with a sleep apnea syndrome. The individual postapneic desaturations were evaluated by a desaturation curve; this curve was built by plotting the fall in SaO2 after an apnea against this apnea's length for each apneic event during the whole night recording. We considered only apneas where the preapneic SaO2 was greater than 90% and the lowest SaO2 value after the apnea was equal to or greater than 60% (limit of linearity of our oximeter). From the desaturation curve, we determined a desaturation surface defined as the area under the curve between 10s and a variable apnea duration. The upper bound used for the determination of the desaturation curve and the desaturation surface was the maximal length of apnea type with the shortest apnea duration between non-REM obstructive apnea and the other apnea types (i.e., obstructive and central apnea, obstructive and mixed apnea, etc.). The desaturation surface was determined separately for non-REM sleep apneas (obstructive apneas, mixed apneas, central apneas, and obstructive apneas with persistent expiratory flow) and REM sleep apnea (all obstructive in type). Non-REM obstructive apneas served as reference to evaluate the severity of apnea-induced desaturations of the other apneas. We found that the desaturation surface of obstructive apnea (OA) with expiratory flow and of REM sleep OA were significantly greater than for OA in non-REM sleep (p less than or equal to 0.005). The OA-related desaturation was significantly greater than those of central apneas (p = 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Role of lung volumes in sleep apnoea-related oxygen desaturation

We studied the influence of lung volumes on apnoea-induced desaturation in ten subjects with sleep apnoea syndrome. Lung volumes were measured by helium dilution in the sitting and supine position and closing volume with the single-breath nitrogen washout test. To characterize the severity of apnoea-induced desaturations, we determined a desaturation curve for each patient. This curve was obtained by plotting the fall in arterial oxygen saturation (SaO2) reached at the end of each apnoea against the apnoea duration. From this curve we selected two indices: 1) the SaO2 fall following 30 s of obstructive apnoea (delta SaO2 30); and 2) the desaturation surface between 10-30 s of obstructive apnoea (DS 10-30). Both the delta SaO2 30 and the DS 10-30 were significantly correlated with the expiratory reserve volume (ERV), measured in the sitting (r = 0.77 and 0.65, respectively; p less than 0.05) and the supine positions (r = 0.96 and 0.87; p less than 0.005). A strong correlation was also observed with the difference between the supine ERV and the seated closing volume CV) (r = 0.99 with delta SaO2 30 and 0.89 with DS 10-30; p less than 0.005). Obesity influenced sitting and supine ERV values. We conclude that, among lung volumes, supine ERV and supine ERV-seated CV are the best indicators of the severity of apnoea-induced desaturation.

Calcium efflux and intracellular exchangeable calcium in mammalian nonmyelinated nerve fibers

Calcium efflux was measured in desheathed rabbit vagus nerves loaded with 45Ca2+. The effects of extracellular calcium, sodium, phosphate, potassium and lanthanum ions on the calcium efflux were investigated and the distribution of intracellular calcium determined by kinetic analysis of 45Ca2+ efflux profiles. The 45Ca2+ desaturation curve can be adequately described by three exponential terms. The rate constant of the first component (0.2 min-1) corresponds to an efflux from an extracellular compartment. The two slow components had rate constants of 0.03 and 0.08 min-1 and represent the efflux from two intracellular pools. The amounts of exchangeable calcium in these two pools, after a loading period of 150 min, were 0.170 and 0.102 mmol/kg wet weight, respectively. The total calcium efflux in physiological conditions amounted to about 24 fmol cm-2 sec-1. The magnitude of the two intracellular compartments as well as the total calcium efflux were markedly affected by extracellular phosphate, sodium and lanthanum, whereas the corresponding rate constants remained almost unchanged. Phosphate reversed the effect of sodium withdrawal on the calcium efflux: in the absence of phosphate, sodium withdrawal increased the calcium efflux to 224%, but in the presence of phosphate, sodium withdrawal decreased calcium efflux to 44%. Phosphate also affected the increase in calcium efflux produced by inhibitors of mitochondrial calcium uptake, suggesting that two different mitochondrial pools contribute to the control and regulation of intracellular calcium and of the transmembrane calcium transport.

Calcium-Transport in Quiescent and 1,25-Dihydroxycholecalciferol-Stimulated Human Osteosarcoma Cells. Role in 24 Hydroxylase Enhancement

The present study evaluates in osteosarcoma cells, the effects of a calcium channel inhibitor nicardipine in 24-hydroxylase activity and 45Ca desaturation curve in presence of 1,25-dihydroxycholecalciferol (1,25(OH)2D3). This sterol induced an increase in 24-OHase activity and 45Ca fluxes. Nicardipine reversed the effect of 1,25(OH)2D3 on 45Ca fluxes but reinforced the enhancement of the 24-OHase activity. The fact that the effects of 1,25(OH)2D3 were reduced by cycloheximide support the hypothesis of a de novo protein synthesis. Our study has allowed us to dissociate the effects of 1,25(OH)2D3 on 24-OHase enhancement from those on Ca2+ transport.

Refined evaluation of the exponential curve parameters and initial exchange rate constant for 22Na+ washout in cultured human skin fibroblasts.

A technique is proposed to evaluate the exponential curve parameters and the initial exchange rate constant (kie) for 22Na+ washout from cultured human skin fibroblasts. After loading with the isotope, the cells were subjected to cold washing and warming steps. A desaturation curve for 22Na+ washout was developed including the activity in the warming medium that corresponded to t = 0 min. Using nonlinear regression analysis, a general three exponential function adequately described the 22Na+ washout in the time interval of 0-70 min. A back extrapolation was performed to estimate the initial time (ti; a negative number) when the total activity was present in the cells. The ti was substituted into the first derivative function of the three exponents to yield the kie. Calculated from the equilibrium distribution of 22Na+ and the specific activity of the medium, the concentration of Na+ (in mM; mean +/- SD) for fibroblasts of two individuals were 13.3 +/- 2.3, n = 3, and 19.0 +/- 5.2, n = 4. This indicates that the washout originated mainly or exclusively from the cellular milieu. Therefore, the kie represents the equilibrium exchange rate constant for Na+ washout from an inhomogeneous cell-related space. Multiple experiments demonstrated that the kie value for the two subjects were significantly higher than the initial slopes of the washout curves (kA), a commonly used parameter to characterize Na+ washout, and significantly lower than the slopes of the fastest exponential components (k3): kie = 0.531 +/- 0.017, kA = 0.502 +/- 0.019, and k3 = 0.557 +/- 0.017 min-1 (n = 3) for one subject, and kie = 0.567 +/- 0.065, kA = 0.479 +/- 0.031, and k3 = 0.667 +/- 0.094 min-1 (n = 6) for the other subject. The respective equilibrium exchange rates for these cells, namely the products of kie and cellular Na+ contents, were 1.10 +/- 0.16 and 1.19 +/- 0.24 nmole/10(5) cells. Using the exponential curve parameters, analytical solutions of a serial model and a parallel model with three compartments were performed. According to these analyses the major portion of the cellular Na+ comprises a fast exchangeable cellular compartment. The relative size of this compartment (expressed as a fraction of total cellular Na+ content) for fibroblasts of the two subjects was 96.2 and 89.2% for the serial model and 96.1 and 89.3% according to the parallel model.(ABSTRACT TRUNCATED AT 250 WORDS)

Efflux of 45Ca from isolated smooth muscle cells of guinea-pig taenia caeci

1. 1. Single smooth muscle cells were isolated from guinea-pig taenia caeci by digestion with collagenase. 2. 2. The 45Ca desaturation curve from isolated cells, which were previously washed with Ca 2+-free solution containing EGTA in Ca 2+-free modified Locke solution, consisted of three components (half-time: 1.0, 3.8 and 12.4 min). 3. 3. The 45Ca efflux from isolated cells in the third component was significantly increased by caffeine. This increase was suppressed by procaine, but was not affected by La 3+. 4. 4. These results suggest that, in guinea-pig taenia caeci, there are at least four Ca 2+ compartments: superficial low and high affinity bound Ca 2+ and cellular low and high affinity bound Ca 2+. Caffeine releases Ca 2+ from the cellular high affinity binding sites.

Vasospasm and regional cerebral blood flow (rCBF) in patients with ruptured intracranial aneurysm: serial rCBF studies with the xenon-133 inhalation method.

To clarify the relationship of vasospasm to the reduction of cerebral blood flow (CBF) and the delayed ischemic neurological deficit, serial rCBF studies with the use of the xenon-133 inhalation method were conducted in 35 postoperative patients with ruptured intracranial aneurysms. The CBF was calculated as an initial slope index (ISI) derived from the desaturation curve of each head probe, and the hemispheric mean value of the ISI (mean ISI) was calculated in both hemispheres. The mean ISI in the hemisphere ipsilateral to the operation was low compared to that of the contralateral hemisphere. In relation to the presence of vasospasm, angiographic findings were classified into the following five types: diffuse, peripheral, proximal-severe, proximal-mild, and no spasm. Patients with vasospasm of the diffuse, peripheral, and proximal-severe types showed a markedly decreased mean ISI, and vasospasm of the diffuse type caused the greatest degree of reduction. The mean ISI of the patients who developed delayed ischemic neurological deficit (DIND) due to vasospasm was significantly decreased (37.4 +/- 4.6) compared to that of the patients who did not develop DIND (52.2 +/- 5.6). None of 3 cases of no spasm and only 1 of 14 cases of proximal-mild spasm developed DIND. On the other hand, all of 4 cases of diffuse, 2 of 3 cases of peripheral, and 2 of 6 cases of proximal-severe spasm developed DIND. Thus, if these three types of vasospasm are joined together as severe vasospasm, 8 of 13 cases with severe vasospasm developed DIND. These results suggest that severe vasospasm causes a reduction of CBF and that the reduced CBF brings about DIND.

Influence of noradrenaline and KCl on calcium translocation in rat vas deferens smooth muscle and its subcellular fractions

1. 1. The calcium desaturation curve of rat vas deferens smooth muscle contained three components. Only 4.4% of total efflux related to the slow intracellular compartment. 2. 2. Although high-KCl and noradrenaline induce contractures in this muscle, their addition during the slow efflux component had little effect on 45Ca efflux. Calcium efflux was, however, stimulated on return to control media after such treatments. 3. 3. Both noradrenaline and KCl initially increased the rate of calcium uptake by muscle strips, but were without significant effect on total uptake. 4. 4. Isolated microsomes and mitochondria from this muscle showed a small passive 45Ca uptake and a much larger ATP-promoted uptake which was Mg 2+-dependent. 5. 5. 45Ca efflux from isolated microsomes and mitochondria was significantly stimulated by KCl or noradrenaline. 6. 6. It is suggested that in the vas deferens, an influx of extracellular calcium possibly coupled with intracellular calcium release provides the calcium to initiate contraction. Relaxation is related to intracellular calcium sequestration along with counterexchange extrusion.

Central nervous system mediated stimulation by thyrotropin-releasing hormone of microcirculation in thyroid gland of rats.

The blood flow of thyroid, adrenal cortex and renal cortex in the pentobarbital anesthetized rat was assessed from hydrogen gas desaturation curve. The microcirculation of thyroid was markedly augmented within 2 min after an intraventricular injection of Thyrotropin-Releasing Hormone (TRH) while Met-Enkephalin (ENK) failed to influence. Both TRH and ENK stimulated the microcirculation of adrenal cortex moderately. ENK diminished the microcirculation of renal cortex whereas TRH did not exert any effect. The response of thyroid to TRH was abolished by vagotomy, thus the existence of a specific TRH-vagus -thyroid connection was indicated.

Some aspects of wetting/dewetting of a porous medium

Various features of wetting/dewetting of porous media are examined. The phenomenon of capillary hysteresis is illustrated by a vertical capillary tube which consists of an alternating sequence of convergent—divergent conical sections. A study of the kinetics of wetting of this tube by a liquid shows that when the velocity of the liquid/vapour meniscus is plotted against the height of penetration, it oscillates about the Washburn velocity—distance curve and performs Haines jumps. A general macroscopic equation is derived for the rate of wetting/dewetting of a porous medium having randomly distributed, finely divided particles or pores. Use is made of the Forchheimer equation, which is an extension of Darcy's equation to higher Reynolds numbers. Dissipative energy terms due to internal fluid calculaton and to irreversible movements of the meniscus strongly affect the initial rate of imbibition, but as the wetting progresses the Reynolds number decreases and Washburn's equation prevails. The application of percolation theory to wetting/dewetting phenomena in porous media is studied. The use of percolation theory by Kirkpatrick and Stinchcombe to find the electrical conductivity of inhomogeneous solid mixtures is adapted to determining the permeability of a porous medium to fluid flow. It is also shown how the relation between the “precolation probability” and the concentration of “unblocked” channels or pores can be applied in calculating the capillary pressure—desaturation curve in drainage. In particular, percolation theory predicts that a threshold pressure or break-through pressure is required before a non-wetting fluid can displace a wetting fluid in a porous medium. It is often convenient to use tree-like or branching lattice networks as models of a porous medium, because these are amenable to exact solutions in regard to percolation probability and permeability. The percolation properties of porous medium models which consist of lattice networks of cylindrical channels with a distribution of cross-sections and also of randomly packed rotund particles are examined and their relevance to wetting/dewetting phenomena discussed.

Movements of labelled sodium ions in isolated rat superior cervical ganglia.

1. Isolated rat superior cervical ganglia were incubated in Krebs solution containing (24)Na and carbachol for 4 min at 25 degrees C. They were then washed at 3 degrees C for 15 min to remove extracellular (24)Na and the efflux of residual intracellular (24)Na stimulated by warming to 25 degrees C.2. During the 15 min wash at 3 degrees C desaturation curves became exponential with a rate constant of 0.012 +/- 0.001 min(-1) (n = 24). This was assumed to represent loss of intracellular (24)Na, and initial uptake of (24)Na was calculated therefrom by back-extrapolation to zero wash-time. After 4 min in (24)Na + 180 muM carbachol intracellular [(24)Na] so calculated was 61.6 +/- 3.1 mM (n = 18), representing 83% labelling of intracellular Na. In the absence of carbachol intracellular [(24)Na] was 10.0 +/- 0.5 mM, representing 49% labelling. Extracellular Na was labelled by > 90% after 4 min in (24)Na. The apparent rate constant for washout of extracellular (24)Na was 0.6 min(-1) at 3 degrees C and 0.95 min(-1) at 25 degrees C.3. The loss of the residual intracellular (24)Na during temperature stimulation was interpreted quantitatively in terms of an exponential decline of the bulk of intracellular (24)Na with an extrusion rate constant of 0.39 +/- 0.1 min(-1) (n = 18), efflux being delayed by passage through the extracellular space with an effective rate constant of 0.8-1.2 min(-1).4. The peak rate constant (k(C)) for the desaturation curve at 25 degrees C was 0.35 +/- 0.01 min(-1). An Arrhenius plot of log k(C)/T degrees K(-1) yielded a two-stage linear regression with a transition at 20 degrees C. Activation energies of 8 and 31 kcal. mole(-1) were calculated above and below this transition respectively.5. Omission of K from the 25 degrees C temperature-stimulating solution reduced k(C) by 62%. The K-sensitive component of extrusion rate constant was a hyperbolic function of [K](e) with half-saturation at 5.6 mM-[K](e) and maximum k(C) of 0.58 min(-1).6. Cyanide (2 mM), 2,4-dinitrophenol (1 mM) and ouabain (1.4 mM) reduced k(C) by 50-90%. The half-maximally inhibiting concentration of ouabain was about 60 muM.7. Substitution of sucrose, Li or choline for external Na did not reduce the extrusion rate of (24)Na in either 6 mM-[K](e) or 0 mM-[K](e). Li stimulated (24)Na extrusion in Na-free, K-free solution.8. The properties of the ganglionic Na pump deduced from rates of temperature-stimulated (24)Na extrusion accord with the view that the ganglion hyperpolarization observed after Na loading by exposure to nicotinic depolarizing agents results from electrogenic Na extrusion. A comparable hyperpolarization is observed after temperature stimulation following Na loading.

A HYDROGEN CATHETER ELECTRODE FOR THE DETERMINATION OF BLOOD FLOW THROUGH ORGAN TISSUE AND CORONARY BLOOD FLOW UNDER CONTINUOUS HYPDXIA

In order to develop an applicable H2 Pt electrode for the determination of average blood flow through organs, a catheter tip electrode covered with a Teflon membrane was designed. The properties of the covered electrode were studied polarographically mainly with reference to the effects of the applied voltage on the linearity, reproducibility and response time of the H2 current against PH2. Next the coronary blood flow was measured by placing an electrode in the coronary sinus and also in the aorta. In a wide range of the applied voltage an addition of H2 to the solution caused an increase in the positive current through the electrodes. But the H2 current was influenced to a considerable extent by the applied voltage. It was observed that a linear relation between the H2 current and PH2 was obtained in a range of applied voltage of -0.1 to +0.3V, when the external resistance was fixed at 5MΩ. However, at the applied voltage of +0.3V the response time was found to be markedly prolonged. Thus, the following conditions were selected as reasonable for practical use in vivo: 1) The platinisation was performed for 10 seconds with -1.5V in an 1% H2 (PtCl6) 6H2O solution with 0.01% Pb (CH3COO) 23H2O, 2) the applied voltage was about -0.1V against an Ag-AgCl electrode, and 3) the external resistance was 5MΩ. Even under these conditions the H2 current was influenced by PO2 the stirring of the medium and the temperature. Therefore, to obtain reproducibility, these factors should be kept unchanged.In order to ascertain the applicability of the present method to blood flow measurement, coronary blood flow was simultaneously determined by use of the H2 and N2O methods. The values obtained by both methods were in fairly good agreement, with only a small difference. The H2 currents alone were then recorded at various inspired PH2's and the coronary blood flow was calculated by using the saturation and desaturation curves of PH2. It was revealed that the change in the inspired PH2 caused no remarkable influence on the calculated value, and that the desaturation curve gave more reliable values for the blood flow than the saturation curve. As an application of this electrode the coronary blood flow was measured under hypoxia over a 2 hour interval. As the result it was shown that the coronary blood flow was significantly increased during continuous hypoxia of over 2 hours compared with that in air respiration.

Effect of local anesthetics on radiocalcium binding in nerve

The effects of the ionized form of dibucaine and the non-ionized form of either dibucaine or benzocaine on the uptake and release of radiocalcium in desheathed frog sciatic nerve were studied. The cationic form of dibucaine, when bound to nerve membrane, reduced significantly the uptake of radiocalcium. The analysis of the kinetics of the desaturation curve revealed that the reduction occurred only in the fast exchangeable compartment for calcium binding in the nerve, which includes the extracellular space, the connective tissue and the surface of the excitable membrane. The fact that radiocalcium uptake in connective tissue (Achilles tendon) was not modified suggests that the cationic form of dibucaine interferes with the binding of calcium ions to readily accessible sites in the nerve fiber. On the other hand, neither benzocaine nor the free base form of dibucaine affected the radiocalcium uptake and release in nerves. Increasing extracellular calcium from 1 mM to 10 mM antagonized the nerve block due to the cationic form of dibucaine, but enhanced the nerve block due to the free base forms of dibucaine and benzocaine. The data support the hypothesis that only the cationic form of tertiary amine local anesthetics interferes with movement of calcium ions to sites governing the increased membrane conductance during nerve excitation.

The regulation of sodium ions in the central nervous system of the herbivorous insect Carausius morosus

1. To test a previously proposed model for ionic regulation (Weidler and Diecke, 1969), the regulation of sodium ions in the central nervous system of the herbivorous insect Carausius morosus was studied with 22Na. 2. The uptake of 22Na is blocked by 5 mM sodium azide in intact, whole nerve cords (Fig. 2, Table 2). From these findings we concluded that sodium ions are actively absorbed by intact nerve cords. 3. When fat-body sheaths are removed, there is no significant difference between the 22Na uptakes of nerve cords bathed in solution containing 5 mM sodium azide and of those not exposed to azide. Upon comparison of these results with those in Fig. 2 and Table 2, we concluded that the active sodium uptake system is located in the fat-body sheath. 4. The desaturation curve of nerve cords completely saturated with 22Na contains the following three components (Fig. 1): a fast component with a half-time of 1.33 min; an intermediate component with a half-time of 0.39 hr; a slow component with a half-time of approximately 2.5 hr. This three-component system conforms to the proposed model with components probably originating in the fat-body sheath space, the extraneural space and the neural space respectively. 5. The size of the fast component is unaffected by metabolic inhibition (Table 2), and it depends on the external sodium concentration (Table 4); therefore we concluded that this component is outside of the active sodium uptake system. Since the site of active sodium uptake was shown to be in the fat-body sheath (probably in the basement membrane), we concluded that this fast component originates in the fat-body sheath space located outside of the basement membrane. 6. Uptakes of 22Na by intact nerve cords for both the slow and intermediate components are significantly decreased when a metabolic inhibitor is present in the bathing medium (Table 2), but sodium uptake for the intermediate component is increased only slightly and that for the slow component not at all when the external sodium concentration is increased from 15 mM to 180 mM. We concluded from these findings that these two components are located within the boundaries of the active sodium uptake system. 7. The half-time of the intermediate component for intact nerve cords metabolically inhibited during the desaturation period was significantly longer than that of uninhibited nerve cords. This result may be explained by the obliteration of the potential difference across the fat-body sheath by the metabolic inhibitor; we concluded that the intermediate component originates in the extraneural space located between the basement membrane of the fat-body sheath and the neural lamella. 8. Since the origins of the fast and intermediate components have been determined, the only logical anatomical site of origin for the slow component is the neural space (i.e., within the confines of the neural lamella). Results are consistent with this hypothesis. 9. Calculations of mean sodium concentrations from space sizes (determined from photomicrographs) and saturated component sizes were consistent with the model and reported values for similar tissues in other animals. Calculated permeabilities for the fat-body sheath and the neural lamella are consistent with previously published viability studies (see Weidler and Diecke, 1969). We concluded that the present study verifies the significant features of the proposed model with regard to sodium ions.

Inert gas diffusion method for measurement of blood flow using saturation techniques. Comparison with directly measured blood flow in isolated gastrocnemius muscle of the cat.

The isolated gastrocnemius muscle of the cat was used to study the relation between the desaturation of 133 xenon measured by external monitoring, and blood flow measured directly by a dropcounter. The metered blood flow agreed with that calculated from the initial slope of the desaturation curve from tissue equilibrated by prolonged intra-arterial infusion and also by atraumatic gas labelling of a local area of the muscle (approximately 0.15% of the muscle weight). In this sense the concept of uniform distribution of blood flow in skeletal muscle has received substantial support. The identity of the results obtained by local gas labelling and by intra-arterial equilibration of the whole muscle with gas implies that there is, at least initially, diffusion equilibrium between tissue and blood in both. However, the clearance curves could in no instance be fitted by a single exponential function. This indicates that the diffusion equilibrium is not maintained after the initial phase. It is suggested that this is not due to the presence of anatomical arteriovenous shunts or other types of uneven perfusion, but to counter current exchange of inert gas through the walls of vessels, i.e. shunting by diffusion explains the shape of the desaturation curves.

Quantitative Evaluation of Local Blood Flow of the Adenohypophysis in Rats1

A method is described for estimating local bloodflowof the pars distalis of anesthetized rats. Flow is computed from the rate of tissue desaturation of hydrogen gas, and repetitive measurements can be made in the same animal. The effect of the portal blood supply on the desaturation curve, and consequently on the measurement of perfusion, is discussed from an analytic viewpoint. It is shown that the extent to which a preceding serial compartment influences the desaturation of a succeeding compartment is dependent on their relative sizes, and that the desaturation of the anterior lobe is not affected significantly by its serially connected compartments. The results indicate that blood flow of the pars distalis is not uniform throughout the gland and that the lack of uniformity may be a consequence of different sources of blood resulting in a flow pattern which is thought to be described by a model consisting of 2 compartments with parallel flows. A slow flow, φI, and a fast flow, φII, especially apparent i...

Effects of arterial carbon dioxide tension and oxygen saturation on cerebral blood flow autoregulation in dogs.

ABSTRACTEffects of arterial carbon dioxide tension and oxygen saturation on cerebral blood flow autoregulation in dogs. Acta physiol. scand. 1965. 66. Suppl. 258. 27–53. ‐ Pressure‐flow relation‐ ships of the cerebral circulation under influence of variations in arterial carbon dioxide tension and oxygen saturation were studied in pentobarbital anaesthetized dogs. Cerebral blood flow was measured by recording of the γ‐ emission of radioactive krypton (Kr85), which was injected into the vertebral artery. The recorded desaturation curve was resolved into two exponential phases and the fast phase was considered as representative of blood flow in the grey matter of the brain. It was demonstrated that autoregulation of flow occurred within wide pressure limits under normo‐ and hypocapnia. Auto‐regulation was less pronounced under hypercapnia and was abolished at low arterial oxygen saturation. Possible mechanisms of autoregulation of cerebral blood flow are discussed. Evidences are presented which speak against the theory that changes in the carbon dioxide tension are the main cause of this autoregulation. The results from previous studies concerning the principal effects of arterial carbon dioxide tension and oxygen saturation on cerebral blood flow were confirmed.

Application of Electrical Resistivity Measurements to Problem of Fluid Flow in Porous Media

The Kozeny equation for fluid flow through isotropic unconsolidated porous media is developed. It is shown that the utility and application of this equation to consolidated and non-isotropic porous media hinge on the derivation of appropriate values for the Kozeny constant, k. It is postulated on the basis of a dichotomy originally suggested by Carman that the Kozeny constant for any porous system can be measured. Electrical methods to determine tortuosity in isotropic, non-isotropic, and partially saturated porous media are outlined and experimental data bearing on the validity of these methods are examined. By combining the fundamental postulates of the Kozeny equation with the properties of the capillary pressure desaturation curve of a porous medium, a new expression for permeability is obtained: [EQUATION] Similarly, the wetting phase relative permeability is shown to be, [EQUATION] Here K is permeability, ^ggr interfacial tension, F formation factor, ^phgr porosity, Sw fractional wetting phase saturation, and Pc capillary pressure. It is noted that the principal difference between unconsolidated and consolidated porous media lies in the higher tortuosities applicable to the latter. By the preparation of thin sections and the use of a statistical method for determining surface area, it is shown that the Kozeny equation appears to give valid surface areas for consolidated porous media. Such measurements make possible an estimate of the average grain sizes of many consolidated porous media.