Interaction between α1B - and other α1 - and α2 -adrenoceptors in producing contractions of mouse spleen

We have investigated the interaction of α₁ - and α₂ -adrenoceptor subtypes in producing isometric contractions to NA in mouse whole spleen. The α₁ -adrenoceptor antagonist prazosin (10^-8 M) or the α₂ -adrenoceptor antagonist yohimbine (10^-6 M) alone produced only small shifts in NA potency in wild type (WT) mice, but the combination produced a large shift in NA potency. In spleen from α_1A/D -KO mice, the effects of prazosin and the combination of prazosin and yohimbine were similar to their effects in WT mice. Hence, in α_1A/D -KO mice, in which the only α₁ -adrenoceptor present is the α_1B -adrenoceptor, prazosin still antagonized contractions to NA. The α_1A -adrenoceptor antagonist RS100329 (3x10^-9 M) produced significant shifts in the effects of higher concentrations of NA (EC₅₀ and EC₇₅ levels) and the α_1D -adrenoceptor antagonist BMY7378 (3x10^-8 M) produced significant shifts in the effects of lower concentrations of NA (EC₂₅ and EC₅₀ levels). The effects of BMY7378 and RS00329 demonstrate α_1D -adrenoceptor and α_1A -adrenoceptor components, and suggest that the α_1B -adrenoceptor interacts with an α_1D -adrenoceptor, and to a lesser extent an α_1A -adrenoceptor, at low, and an α_1A -adrenoceptor at high, NA concentrations. This study demonstrates the complex interaction between α₁ - and α₂ -adrenoceptor subtypes in producing contractions of mouse spleen and may have general implications for α-adrenoceptor mediated control of smooth muscle.

Enhanced splenic volume and contraction in elite endurance athletes

Splenic contraction, which leads to ejection of stored erythrocytes, is greater in athletes involved in regular freediving or high-altitude activities. As this response facilitates oxygen-carrying capacity, similar characteristics may be expected of elite endurance athletes. Therefore, our aims were to compare resting and apnea-induced splenic volume in endurance athletes and untrained individuals, and to assess the athletes' exercise-induced splenic volume. Twelve elite biathletes (7 women) and 12 controls (6 women) performed a maximal effort apnea in a seated position. In addition, the biathletes completed a maximal roller-skiing time trial. Splenic dimensions were measured by ultrasonic imaging for subsequent volume calculations, whereas Hb was analyzed from capillary blood samples and cardiorespiratory variables were monitored continuously. Baseline splenic volume was larger in the biathletes (214 ± 56 mL) compared with controls (157 ± 39 mL, P = 0.008) and apnea-induced splenic contraction was also greater in the biathletes (46 ± 20 mL vs. 30 ± 16 mL, P = 0.035). Hb increased immediately after apnea in the biathletes (4.5 ± 4.8%, P = 0.029) but not in the controls (-0.7 ± 3.1%, P = 0.999). Increases in exercise-induced splenic contraction (P = 0.008) and Hb (P = 0.001) were greater compared with the apnea-induced responses among the athletes. Baseline splenic volume tended to be correlated with V̇o_2max (r = 0.584, P = 0.059). We conclude that elite biathletes have greater splenic volume with a greater ability to contract and elevate Hb compared with untrained individuals. These characteristics may transiently enhance O₂-carrying capacity and possibly increase O₂ uptake, thereby helping biathletes to cope with high intermittent O₂ demands and severe O₂ deficits that occur during biathlon training and competition.NEW & NOTEWORTHY This study demonstrates that elite biathletes have larger splenic volume, apnea-induced splenic contraction, and Hb elevation compared with untrained individuals, which is likely functional to cope with high O₂ demands and substantial O₂ deficits. We believe that enhanced splenic contraction may be of importance during competitions involving cross-country skiing, to regulate circulating Hb and enhance O₂-carrying capacity, which may protect [Formula: see text] and increase O₂ uptake.

Systolic reserve maintains left ventricular-vascular coupling when challenged by adverse breathing mechanics and hypertension in healthy adults

Augmented negative intrathoracic pressures (nITP) and dynamic hyperinflation (DH) are adverse breathing mechanics (ABM) associated with chronic obstructive pulmonary disease (COPD) that attenuate left ventricular (LV) preload and augment afterload. In COPD, hypertension (elevated systemic arterial load) commonly adds additional afterload to the LV. Combined ABM and hypertension may profoundly challenge ventricular-vascular coupling and attenuate stroke volume (SV), particularly if LV systolic reserve is limited. However, even in the healthy heart, the combined impact of ABM and systemic arterial loading on LV function and ventricular-vascular coupling has not been fully elucidated. Healthy volunteers (10 M/9 F, 24 ± 3 yr old) were challenged with mild (-10 cmH₂O nITP and 25% DH) and severe (-20 cmH₂O nITP and 100% DH) ABM, without and with postexercise ischemia (PEI) at each severity. LV SV, chamber geometry, end-systolic elastance (E_es), arterial elastance (E_a), and ventricular-vascular coupling (E_es:E_a) were quantified using echocardiography. Compared with resting control (58 ± 13 mL), SV decreased during mild ABM (51 ± 13 mL), mild ABM + PEI (51 ± 11 mL), severe ABM (50 ± 12 mL), and severe ABM + PEI (47 ± 11 mL) (P < 0.001); similar trends were observed for LV end-diastolic volume. The end-diastolic radius of septal curvature increased, indicating direct ventricular interaction, during severe ABM and severe ABM + PEI (P < 0.001). Compared with control (1.99 ± 0.41 mmHg/mL), E_a increased progressively with mild ABM (2.21 ± 0.47 mmHg/mL) and severe ABM (2.50 ± 0.56 mmHg/mL); at each severity, E_a was greater with superimposed PEI (P < 0.001). However, well-matched E_es increases occurred, and E_es:E_a was unchanged throughout. ABM pose a challenge to ventricular-vascular coupling that is accentuated by superimposed PEI; however, in healthy younger adults, the LV has substantial systolic reserve to maintain coupling.NEW & NOTEWORTHY In healthy younger adults, combined dynamic hyperinflation (DH) and negative intrathoracic pressures (nITP) attenuate left ventricular filling, but through different mechanisms at different severities. DH and nITP contribute to increased left ventricular afterload through mechanical effects in addition to presumed reflexive regulation, which can be further increased by elevated arterial loading. However, within this demographic, the left ventricle has substantial reserve to increase systolic performance, which matches contractility to afterload to preserve stroke volume.

Splenic contraction is enhanced by exercise at simulated high altitude

Purpose

Splenic contraction increases circulating hemoglobin (Hb) with advantages during hypoxia. As both hypoxia and exercise have been shown to be important separate triggers of splenic contraction we aimed to investigate if the spleen response to simulated high altitude (HA) is enhanced by superimposing exercise.

Method

Fourteen healthy volunteers (seven females) performed the following protocol in a normobaric environment sitting on an ergometer cycle: 20 min rest in normoxia; 20 min rest while breathing hypoxic gas simulating an altitude of 3500 m; 10 min exercise at an individually set intensity while breathing the hypoxic gas; 20 min rest in hypoxia; and finally 20 min rest in normoxia. Spleen measurements were collected by ultrasonic imaging and venous Hb measured at the end of each intervention.

Result

Mean ± SD baseline spleen volume during normoxic rest was 280 ± 107 mL, the volume was reduced by 22% during rest in hypoxia to 217 ± 92 mL (p < 0.001) and by 33% during exercise in hypoxia (189 mL; p < 0.001). Hb was 140.7 ± 7.0 g/L during normoxic rest and 141.3 ± 7.4 g/L during hypoxic rest (NS), but increased by 5.3% during hypoxic exercise (148.6 ± 6.3 g/L; p < 0.001). Spleen volume and Hb were stepwise changed back to baseline at cessation of exercise and return to normoxia.

Conclusion

Splenic contraction is induced by hypoxia and further enhanced by superimposing exercise, and reduced when exercise ceases, in a step-wise manner, showing that the tonic but partial contraction observed in long-term field expeditions to HA may occur also in the short term. This “graded response” may be beneficial during acclimatization to HA, to cope with moderate chronic hypoxia during rest while allowing additional enhancement of oxygen carrying capacity to overcome short bouts of extreme hypoxia caused by exercise.

Both α1B- and α1A-adrenoceptor subtypes are involved in contractions of rat spleen

BACKGROUND

The spleen is a reservoir for circulating blood cells, and can contract to expel them.

METHODS

We have investigated the adrenoceptors involved in isometric contractions of rat spleen produced by noradrenaline (NA) and the α₁-adrenoceptor agonist phenylephrine (Phe).

RESULTS

Contractions to NA were antagonized by both the α₁-adrenoceptor antagonist prazosin (10^-8 M) and the α₂-adrenoceptor antagonist yohimbine (10^-6M), and the combination produced further shifts in NA potency. Contractions to Phe were antagonized by prazosin (10^-8 M) which caused a marked parallel shift in the concentration-response curve. High non-selective concentrations of the α_1D-adrenoceptor antagonist BMY7378 (10^-6 M), the α_1A-adrenoceptor antagonist RS100329 ((3 × 10^-8 M), and the putative α_1B-adrenoceptor antagonist cyclazosin (10^-8 M) also produced parallel shifts in the Phe concentration-response curve. BMY7378 at the selective concentration of 3 × 10^-8 M had no effect on responses to Phe, but RS100329 in the selective concentration of 3 × 10^-9 M produced a marked shift in the effects of high concentrations of Phe. Hence, antagonists in concentrations that block both α_1A- and α_1B-adrenoceptors produce approximately parallel shifts in Phe potency.

CONCLUSIONS

Contractions of rat spleen to adrenergic agonists involve α₂- and α_1B-adrenoceptors, with a lesser role for α_1A-adrenoceptors. This confirms the suggestion that smooth muscle contractions commonly involve multiple subtypes.

Towards an understanding of the physical activity-BDNF-cognition triumvirate: A review of associations and dosage

Physical activity has received substantial research attention due to its beneficial impact on cognition in ageing, particularly via the action of brain-derived neurotrophic factor (BDNF). It is well established that physical activity can elevate circulating levels of BDNF, and that BDNF has neurotrophic, neuroprotective and cognitively beneficial properties. Yet, practical implementation of this knowledge is limited by a lack of clarity on context and dose-effect. Against a shifting backdrop of gradually diminishing physical and cognitive capacity in normal ageing, the type, intensity, and duration of physical activity required to elicit elevations in BDNF, and more importantly, the magnitude of BDNF elevation required for detectable neuroprotection remains poorly characterised. The purpose of this review is to provide an overview of the association between physical activity, BDNF, and cognition, with a focus on clarifying the magnitude of these effects in the context of normative ageing. We discuss the implications of the available evidence for the design of physical activity interventions intended to promote healthy cognitive ageing.

Spleen Size and Function in Sherpa Living High, Sherpa Living Low and Nepalese Lowlanders

High-altitude (HA) natives have evolved some beneficial responses leading to superior work capacity at HA compared to native lowlanders. Our aim was to study two responses potentially protective against hypoxia: the spleen contraction elevating hemoglobin concentration (Hb) and the cardiovascular diving response in Sherpa highlanders, compared to lowlanders. Male participants were recruited from three groups: (1) 21 Sherpa living at HA (SH); (2) seven Sherpa living at low altitude (SL); and (3) ten native Nepalese lowlanders (NL). They performed three apneas spaced by a two-min rest at low altitude (1370 m). Their peripheral oxygen saturation (SpO₂), heart rate (HR), and spleen volume were measured across the apnea protocol. Spleen volume at rest was 198 ± 56 mL in SH and 159 ± 35 mL in SL (p = 0.047). The spleen was larger in Sherpa groups compared to the 129 ± 22 mL in NL (p < 0.001 compared to SH; p = 0.046 compared to SL). Spleen contraction occurred in all groups during apnea, but it was greater in Sherpa groups compared to NL (p < 0.001). HR was lower in Sherpa groups compared to NL both during rest (SL: p < 0.001; SH: p = 0.003) and during maximal apneas (SL: p < 0.001; SH: p = 0.06). The apnea-induced HR reduction was 8 ± 8% in SH, 10 ± 4% in SL (NS), and 18 ± 6% in NL (SH: p = 0.005; SL: p = 0.021 compared to NL). Resting SpO₂ was similar in all groups. The progressively decreasing baseline spleen size across SH, SL, and NL suggests a role of the spleen at HA and further that both genetic predisposition and environmental exposure determine human spleen size. The similar HR responses of SH and SL suggest that a genetic component is involved in determining the cardiovascular diving response.

The Magnitude of Diving Bradycardia During Apnea at Low-Altitude Reveals Tolerance to High Altitude Hypoxia

Acute mountain sickness (AMS) is a potentially life-threatening illness that may develop during exposure to hypoxia at high altitude (HA). Susceptibility to AMS is highly individual, and the ability to predict it is limited. Apneic diving also induces hypoxia, and we aimed to investigate whether protective physiological responses, i.e., the cardiovascular diving response and spleen contraction, induced during apnea at low-altitude could predict individual susceptibility to AMS. Eighteen participants (eight females) performed three static apneas in air, the first at a fixed limit of 60 s (A1) and two of maximal duration (A2-A3), spaced by 2 min, while SaO₂, heart rate (HR) and spleen volume were measured continuously. Tests were conducted in Kathmandu (1470 m) before a 14 day trek to mount Everest Base Camp (5360 m). During the trek, participants reported AMS symptoms daily using the Lake Louise Questionnaire (LLQ). The apnea-induced HR-reduction (diving bradycardia) was negatively correlated with the accumulated LLQ score in A1 (r _s = -0.628, p = 0.005) and A3 (r _s = -0.488, p = 0.040) and positively correlated with SaO₂ at 4410 m (A1: r = 0.655, p = 0.003; A2: r = 0.471, p = 0.049; A3: r = 0.635, p = 0.005). Baseline spleen volume correlated negatively with LLQ score (r _s = -0.479, p = 0.044), but no correlation was found between apnea-induced spleen volume reduction with LLQ score (r _s = 0.350, p = 0.155). The association between the diving bradycardia and spleen size with AMS symptoms suggests links between physiological responses to HA and apnea. Measuring individual responses to apnea at sea-level could provide means to predict AMS susceptibility prior to ascent.

Changes in Splenic Volume After the Treadmill Exercise at Specific Workloads in Elite Long-Distance Runners and Recreational Runners

Introduction:

Spleen acts as blood reservoir both in animals and human beings. Spleen contracts during the exercise and so augment the systemic circulation and helps body to maintain longer on high intensity exercise. Reviewing all available literature, the human spleen shows a decrease in volume, in range from 8% to 56%, depending on the work intensity.

Aim:

To evaluate the percentage of the decrease in splenic volume after the treadmill exercise at specific workloads: aerobic threshold intensity, anaerobic threshold intensity, submaximal intensity and maximal intensity.

Methods:

This prospective study with repeated measurements included 16 healthy subjects, divided in two groups. First group consisted of 8 elite long-distance runners and second group of 8 recreational runners. First testing consisted of treadmill ergospirometry test. This data was crucial for the second testing where subjects were exercising on treadmill at specific workloads. Four specific workloads were determined: treadmill exercise at aerobic threshold intensity (1st workload), anaerobic threshold intensity (2nd workload), submaximal intensity (3rd workload) and maximal intensity (4th workload). Workloads were controlled by the speed of treadmill, for each subject individually regarding the ergospirometry test. Ultrasound measurement of spleen was done before and after each workload.

Results:

Elite long-distance runners showed greater spleen contraction than recreational runners after four workloads. Spleen contraction was the biggest after the 3rd workload in elite long-distance runners. Smallest contraction was in group of recreational runners after the 1st workload. Statistically significant difference was not found between the groups, regarding the splenic volume after exercise at four specific workloads (p>0.05).

Conclusion:

Elite long-distance runners had greater decrease in splenic volume than recreational runners, after exercise at four specific workloads, without significant difference. Greatest decrease happened in elite long-distance runners, after exercise at submaximal intensity - 49% decrease in splenic volume.

Spleen reactivity during incremental ascent to altitude

The spleen contains a reservoir of red blood cells that are mobilized into circulation when under physiological stress. Despite the spleen having an established role in compensation to acute hypoxia, no previous work has assessed the role of the spleen during ascent to high altitude. Twelve participants completed 2 min of handgrip exercise at 30% of maximal voluntary contraction at 1,045, 3,440, and 4,240 m. In a subset of eight participants, an infusion of phenylephrine hydrochloride was administered at a dosage of 30 µg/l of predicted blood volume at each altitude. The spleen was imaged by ultrasound via a 2- to 5.5-MHz curvilinear probe. Spleen volume was calculated by the prolate ellipsoid formula. Finger capillary blood samples were taken to measure hematocrit. Spleen images and hematocrit were taken both before and at the end of both handgrip and phenylephrine infusion. No changes in resting spleen volume were observed between altitudes. At low altitude, the spleen contracted in response to handgrip [272.8 ml (SD 102.3) vs. 249.6 ml (SD 105.7), P = 0.009], leading to an increase in hematocrit (42.6% (SD 3.3) vs. 44.3% (SD 3.3), P = 0.023] but did not contract or increase hematocrit at the high-altitude locations. Infusion of phenylephrine led to spleen contraction at all altitudes, but only lead to an increase in hematocrit at low altitude. These data reveal that the human spleen may not contribute to acclimatization to chronic hypoxia, contrary to its response to acute sympathoexcitation. These results are explained by alterations in spleen reactivity to increased sympathetic activation at altitude. NEW & NOTEWORTHY The present study demonstrated that, despite the known role of the human spleen in increasing oxygen delivery to tissues during acute hypoxia scenarios, the spleen does not mobilize red blood cells during ascent to high altitude. Furthermore, the spleen's response to acute stressors at altitude depends on the nature of the stressor; the spleen's sensitivity to neurotransmitter is maintained, while its reflex response to stress is dampened.

Exercise and circulating BDNF: Mechanisms of release and implications for the design of exercise interventions

Engagement in regular bouts of exercise confers numerous positive effects on brain health across the lifespan. Acute bouts of exercise transiently improve cognitive function, while long-term exercise training stimulates brain plasticity, improves brain function, and helps to stave off neurological disease. The action of brain-derived neurotrophic factor (BDNF) is a candidate mechanism underlying these exercise-induced benefits and is the subject of considerable attention in the exercise-brain health literature. It is well established that acute exercise increases circulating levels of BDNF and numerous studies have sought to characterize this response for the purpose of improving brain health. Despite the interest in BDNF responses to exercise, little focus has been given to understanding the sources and mechanisms that underlie this response for the purpose of deliberately increasing circulating levels of BDNF. Here we review evidence to support that exploiting these mechanisms of BDNF release can help to optimize brain plasticity outcomes via exercise interventions, which could be especially relevant in the context of multimodal training (i.e., exercise and cognitive stimulation). Therefore, the purpose of this paper is to review the candidate sources of BDNF during exercise and the mechanisms of release. As well, we discuss strategies for maximizing BDNF responses to exercise, and propose novel research directions for advancing our understanding of these mechanisms.

Short-Duration Maximal and Long-Duration Submaximal Effort Forearm Exercise Achieve Elevations in Serum Brain-Derived Neurotrophic Factor

Brain-derived neurotrophic factor (BDNF) is a major orchestrator of exercise-induced brain plasticity and circulating (peripheral) BDNF may have central effects. Approximately 99% of circulating BDNF is platelet-bound, and at rest ~30% of circulating platelets are stored in the spleen. Interestingly, forearm handgrip exercise significantly elevates sympathetic outflow and has been shown to induce splenic constriction, suggesting that small muscle mass exercise could stand as a viable strategy for increasing circulating BDNF; however, the BDNF response to handgrip exercise is currently unknown. Purpose: This study examined BDNF and platelet responses to short-duration maximal (ME) and prolonged submaximal (SE) effort handgrip exercise. Methods: Healthy males (n = 18; 21.4 ± 2.1 years, BMI 25.0 ± 1.0 kg/m²) performed 10 min of ME and 30 min of SE. Blood was sampled for the determination of serum BDNF and platelet count at rest and during the last minute of exercise. Results: Compared to rest, serum BDNF significantly increased during ME (21.2%) and SE (11.2%), which displayed a non-significant trend toward an intensity-dependent response. Platelets increased in an intensity-dependent fashion compared to rest with an 8.0% increase during ME and 3.1% during SE, and these responses were significantly correlated with diastolic blood pressure responses to handgrip exercise. Further, the amount of BDNF per platelet significantly increased compared to rest during ME (13.4%) and SE (8.7%). Conclusions: Handgrip exercise evokes significant increases in serum BDNF and platelets, implicating splenic constriction as a key mechanism and confirming efficacy of this exercise model for elevating circulating BDNF.

Responses of the human spleen to exercise

The human spleen shows a decrease in volume of around 40% early during vigorous exercise and in response to other stressful stimuli such as maximal apnoea and the breathing of hypoxic gas mixtures. Contraction seems an active response, mediated by alpha-adrenergic fibres in the splenic nerve. Given the relatively small size of the human spleen, the effect upon physical performance is likely to be small; the augmentation of total blood volume is <2%, and even taking account of other causes of haemoconcentration during vigorous exercise, the increase of haematocrit is <10%. However, one of two studies suggested that the haemoconcentration may be sufficient to cause errors in the traditional method for calculating exercise-induced changes of plasma volume. The spleen also contributes leucocytes and platelets to the general circulation as part of the "fight or flight" reaction to stressors. The mobilisation of leucocytes proceeds more slowly than that of the red cells; it depends not only upon an active contraction of the spleen, but also a modulation of leucocyte adhesion molecules. Splenectomy impairs exercise performance in horses, but human performance data are lacking; overall health effects seem minimal, and many patients live many years after removal of their spleens.

Effects of portal hypertension on contractility of rat spleen

Portal hypertension induces changes in vascular responses to vasoconstrictors. However, the effects of portal hypertension on splenic contraction have not previously been investigated. In partial portal vein ligated (PVL) and sham-operated rats, we examined the splenic contractile responses to cumulative concentrations of noradrenaline and KCl. In PVL rats, the potency of noradrenaline in producing splenic contraction was significantly increased (pEC50 of 5.88 ± 0.08), as compared to sham (5.40 ± 0.06; p<0.001). In the presence of prazosin (10(-8)M), there was a significant rightward shift in the noradrenaline concentration response curve but the shift was greater for PVL, so that in the presence of prazosin there was no significant difference between PVL and sham animals in the potency of noradrenaline. Prazosin produced a significantly greater shift of noradrenaline potency in spleen from PVL (pKB of 8.88 ± 0.06) (n=6) than from sham animals (8.51 ± 0.08, n=6), demonstrating that the α1-adrenoceptor mediated component is greater in spleen from PVL. In the presence of prazosin (10(-8)M) the residual response is non-α1-adrenoceptor mediated, presumably α2-adrenoceptor mediated, and this response did not differ between sham and PVL. The maximum splenic contraction did not significantly differ between sham and PVL rats for either agonist. In conclusion, noradrenaline potency in contracting the rat spleen was significantly increased in tissues from PVL rats. The increased potency of prazosin suggests a greater predominance of α1-adrenoceptors in spleen of PVL rats, as prazosin has lower potency at α2-adrenoceptors.

Superficial venous vascular response of the resting limb during static exercise and postexercise muscle ischemia

Superficial venous vascular response to exercise is mediated sympathetically, although the mechanism is not fully understood. We examined whether sympathetic activation via muscle metaboreflex plays a role in the control of a superficial vein in the contralateral resting limb during exercise. The experimental condition involved selective stimulation of muscle metaboreceptors: 12 subjects performed static handgrip exercises at 45% maximal voluntary contraction for 1.5 min followed by a recovery period with arterial occlusion of the exercise arm (OCCL). For the control condition (CONT), the same exercise protocol was performed except that the recovery period occurred without arterial occlusion. Heart rate (HR) and mean arterial blood pressure (MAP) were measured. The cross-sectional area of the basilic superficial vein (CSAvein) and blood velocity (Vvein) in the resting upper arm were measured by ultrasound while the cuff on resting upper arm was inflated constantly to a subdiastolic pressure of 50 mm Hg. Basilic vein blood flow (BFvein) was calculated as CSAvein × Vvein. During exercise under both OCCL and CONT, HR and MAP increased (p < 0.05), while CSAvein decreased (p < 0.05). During recovery under OCCL, HR returned to baseline, but the exercise-induced increase in MAP and decrease in CSAvein were maintained (p < 0.05). During recovery under CONT, HR, MAP, and CSAvein returned to baseline. BFvein did not change during exercise or recovery under either condition. These results suggest that sympathoexcitation via muscle metaboreflex may be one of the factors responsible for exercise-induced constriction of the superficial veins per se in the resting limb.

Effect of Breath Holding on Spleen Volume Measured by Magnetic Resonance Imaging

Objective

Ultrasonographic studies have demonstrated transient reduction in spleen volume in relation to apnea diving. We measured spleen volume under various respiratory conditions by MR imaging to accurately determine the influence of ordinary breath holding on spleen volumetry.

Materials and Methods

Twelve healthy adult volunteers were examined. Contiguous MR images of the spleen were acquired during free breathing and during respiratory manipulations, including breath holding at the end of normal expiration, breath holding at deep inspiration, and the valsalva maneuver, and spleen volume was measured from each image set based on the sum-of-areas method. Acquisition during free breathing was performed with respiratory triggering. The duration of each respiratory manipulation was 30 s, and five sets of MR images were acquired serially during each manipulation.

Results

Baseline spleen volume before respiratory manipulation was 173.0 ± 79.7 mL, and the coefficient of variance for two baseline measures was 1.4% ± 1.6%, suggesting excellent repeatability. Spleen volume decreased significantly just after the commencement of respiratory manipulation, remained constant during the manipulation, and returned to the control value 2 min after the cessation of the manipulation, irrespective of manipulation type. The percentages of volume reduction were 10.2% ± 2.9%, 10.2% ± 3.5%, and 13.3% ± 5.7% during expiration breath holding, deep-inspiration breath holding, and the valsalva maneuver, respectively, and these values did not differ significantly.

Conclusions

Spleen volume is reduced during short breath-hold apnea in healthy adults. Physiological responses of the spleen to respiratory manipulations should be considered in the measurement and interpretation of spleen volume.

Effects of a TASER® conducted energy weapon on the circulating red-blood-cell population and other factors in Sus scrofa

In previous studies hematocrit has been consistently increased in an anesthetized animal model after exposures to TASER(®) conducted energy weapons (CEWs). In the present study we analyzed changes in blood cell counts and red blood cell membrane proteins following two 30-s applications of a TASER C2 device (which is designed for civilian use). Hematocrit increased significantly from 33.2 ± 2.4 (mean ± SD) to 42.8 ± 4.6 % immediately after CEW exposure of eleven pigs (Sus scrofa). Red blood cell count increased significantly from 6.10 ± 0.55 × 10(12)/L to 7.45 ± 0.94 × 10(12)/L, and mean corpuscular volume increased significantly from 54.5 ± 2.4 fl to 57.8 ± 2.6 fl. Mean corpuscular hemoglobin concentration decreased significantly from 20.5 ± 0.7 to 18.5 ± 0.6 mM. Thirty protein spots (from two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis, selected for detailed comparison) exhibited greater densities 30-min post-exposure compared with pre-exposure values. A greater number of echinocytes were observed following CEW exposure. On the basis of these results it appears that, during the strong muscle contractions produced by TASER CEWs, a specific population of red blood cells (RBCs) may be released from the spleen or other reservoirs within the body. The total time of CEW exposure in the present study was relatively long compared with exposures in common law-enforcement scenarios. Despite statistically significant changes in red blood cell counts (and other measures directly related to RBCs), the alterations were short-lived. The transient nature of the changes would be likely to counteract any potentially detrimental effects.

Pulsed high oxygen induces a hypoxic-like response in human umbilical endothelial cells and in humans

It has been proposed that relative changes of oxygen availability, rather than steady-state hypoxic or hyperoxic conditions, play an important role in hypoxia-inducible factor (HIF) transcriptional effects. According to this hypothesis describing the "normobaric oxygen paradox", normoxia following a hyperoxic event is sensed by tissues as an oxygen shortage, upregulating HIF-1 activity. With the aim of confirming, at cellular and at functional level, that normoxia following a hyperoxic event is "interpreted" as a hypoxic event, we report a combination of experiments addressing the effects of an intermittent increase of oxygen concentration on HIF-1 levels and the activity level of specific oxygen-modulated proteins in cultured human umbilical vein endothelial cells and the effects of hemoglobin levels after intermittent breathing of normobaric high (100%) and low (15%) oxygen in vivo in humans. Our experiments confirm that, during recovery after hyperoxia, an increase of HIF expression occurs in human umbilical vein endothelial cells, associated with an increase of matrix metalloproteinases activity. These data suggest that endothelial cells "interpret" the return to normoxia after hyperoxia as a hypoxic stimulus. At functional level, our data show that breathing both 15 and 100% oxygen 30 min every other day for a period of 10 days induces an increase of hemoglobin levels in humans. This effect was enhanced after the cessation of the oxygen breathing. These results indicate that a sudden decrease in tissue oxygen tension after hyperoxia may act as a trigger for erythropoietin synthesis, thus corroborating the hypothesis that "relative" hypoxia is a potent stimulator of HIF-mediated gene expressions.

Non-alpha-adrenergic effects on systemic vascular conductance during lower-body negative pressure, static exercise and muscle metaboreflex activation

AIM

This study tested the hypothesis that non-α-adrenergic mechanisms contribute to systemic vascular conductance (SVC) in a reflex-specific manner during the sympathoexcitatory manoeuvres.

METHODS

Twelve healthy subjects underwent lower-body negative pressure (LBNP, -40 mmHg) as well as static handgrip exercise (HG, 20% of maximal force) followed by post-exercise forearm circulatory occlusion (PECO, 5 min each) with and without α-adrenergic blockade induced by phentolamine (PHE). Aortic blood flow, finger blood pressure and superficial femoral artery blood flow were measured to calculate cardiac output, SVC and leg vascular conductance (LVC) during the last minute of each intervention.

RESULTS

Mean arterial pressure (MAP) decreased more during LBNP with PHE compared with saline (-7 ± 7 vs. -2 ± 5%, P = 0.016). PHE did not alter the MAP response to HG (+20 ± 12 and +24 ± 16%, respectively, for PHE and saline) but decreased the change in MAP during PECO (+12 ± 7 vs. +21 ± 14%, P = 0.005). The decrease in SVC and LVC with LBNP did not differ between saline and PHE trials (-13 ± 10 vs. -17 ± 10%, respectively, for SVC, P = 0.379). In contrast, the SVC response to HG increased from -9 ± 12 with saline to + 5 ± 15% with PHE (P = 0.002) and from -16 ± 15 with saline to +1 ± 16% with PHE during PECO (P = 0.003). LVC responses to HG or PECO were not different from saline with PHE.

CONCLUSIONS

Non-α-adrenergic vasoconstriction was present during LBNP. The systemic vasoconstriction during static exercise and isolated muscle metaboreflex activation, in the absence of leg vasoconstriction, was explained by an α-adrenergic mechanism. Therefore, non-α-adrenergic vasoconstriction is more emphasized during baroreflex, but not metaboreflex-mediated sympathetic activation.

Cortical circuitry associated with reflex cardiovascular control in humans: does the cortical autonomic network "speak" or "listen" during cardiovascular arousal

Beginning with clinical evidence of fatal cardiac arrhythmias in response to severe stress, in epileptic patients, and following stroke, the role of the cerebral cortex in autonomic control of the cardiovascular system has gained both academic and clinical interest. Studies in anesthetized rodents have exposed the role of several forebrain regions involved in cardiovascular control. The introduction of functional neuroimaging techniques has enabled investigations into the conscious human brain to illuminate the temporal and spatial activation patterns of cortical regions that are involved with cardiovascular control through the autonomic nervous system. This symposia report emphasizes the research performed by the authors to understand the functional organization of the human forebrain in cardiovascular control during physical stressors of baroreceptor unloading and handgrip exercise. The studies have exposed important associations between activation patterns of the insula cortex, dorsal anterior cingulate, and the medial prefrontal cortex and cardiovascular adjustments to physical stressors. Furthermore, these studies provide functional anatomic evidence that sensory signals arising from baroreceptors and skeletal muscle are represented within the insula cortex and the medial prefrontal cortex, in addition to the sensory cortex. Thus, the cortical pathways subserving reflex cardiovascular control integrate viscerosensory inputs with outgoing traffic that modulates the autonomic nervous system.

Increased hematocrit after applications of conducted energy weapons (including TASER(®) devices) to Sus scrofa

Conducted energy weapons (CEWs) are used by law enforcement personnel to incapacitate individuals quickly and effectively, without intending to cause lethality. CEWs have been deployed for relatively long or repeated exposures in some cases. In laboratory animal models, central venous hematocrit has increased significantly after CEW exposure. Even limited applications (e.g., three 5-sec applications) resulted in statistically significant increases in hematocrit. Preexposure hematocrit was significantly higher in nonsurvivors versus survivors after more extreme CEW applications. The purpose of this technical note is to address specific questions that may be generated when examining these results. Comparisons among results of CEW applications, other electrical muscle stimulation, and exercise/voluntary muscle contraction are included. The anesthetized swine appears to be an acceptable animal model for studying changes in hematocrit and associated red blood cell changes. Potential detrimental effects of increased hematocrit, and considerations during law enforcement use, are discussed.