By H. Rendell. North Carolina State University.
Because vibrissa resonance prop- erties vary systematically across the face of a rat discount 30 mg procardia otc cardiovascular system nursing assessment, with lower frequencies represented more posteriorly and higher frequencies represented more anteriorly discount procardia 30mg with mastercard capillaries around the eyes, a map of frequen- cies is observed across SI with a system of isofrequency columns extending along arcs of vibrissae. These ﬁndings support the hypothesis that a place code exists for the representation of frequency information in this system, by which an increase in mean ﬁring rate in a speciﬁc position within a map indicates the frequency of stimulation. In the fourth section of this chapter, we discuss how active sensory processes may impact perception employed by vibrissa resonance. In the ﬁfth section of this chapter, we provide evidence that vibrissa resonance not only contributes to a mean ﬁring rate code and place code, but may also contribute to temporal coding of frequency information, considered over broad and ﬁne tem- poral scales. Following the onset of a stimulus, vibrissa resonance has a relatively slow rise time, requiring tens of milliseconds to reach the full ampliﬁcation of motion. Correspondingly, more optimal neural frequency tuning is observed at longer latencies after stimulus initiation (e. This ﬁnding suggests that initial neural activity may encode object contact and the somatotopic position of vibrissa deﬂection, while longer-latency activity may convey frequency speciﬁc information. We provide evidence from peripheral and SI recordings that the high frequencies, in the hundreds of Hertz (Hz), transmitted by vibrissae at their funda- mental resonance frequency can drive high ﬁdelity neural activity. These ﬁndings suggest that a volley principle may exist in the transmission of high resolution temporal signals from the periphery. Speciﬁcally, the sensitivity of this system to high velocity vibrissa motion, and the high degree of direction tuning observed in many trigeminal neurons, suggest that an inherent frequency doubling may occur through the convergence of signals from direction-tuned peripheral neurons. In the ﬁnal section of this chapter, we summarize the main ﬁndings and give a brief discussion of how the principles described here may relate to human tactile perception. THE BEHAVIORAL RELEVANCE OF HIGH FREQUENCY SOMATOSENSORY PERCEPTION Frequency information approximately tens of Hz to over a kHz is essential to accurate sensory processing in the auditory, somatosensory, and visual domains. The soma- tosensory system employs frequency-speciﬁc information in a variety of perceptual contexts. Vibratory stimuli transmitted through solid media provide an important sensory input to a variety of mammalian species. For example, blind moles are known to seek out conspeciﬁcs and termite colonies using primarily vibratory cues transmitted through the ground. High frequency, temporally varying information also directly beneﬁts human tactile perception. Surface perception in humans may employ temporally varying signals related to vibration perception. While spatially intensive cues dominate the judgment of roughness for surfaces with a periodicity in the range of ~1–3 mm,4,5 temporal frequency information likely contributes to the judgment of spatial © 2005 by Taylor & Francis Group. For example, robust tactile apparent motion illusions can be evoked when speciﬁc frequencies of stimulation, typically ≥50 Hz, are applied either sequentially across a series of three or more contact points or in bursts applied to >2 contact points. Cockroaches can discriminate between laminar airﬂow of the type generated by wind from turbulent airﬂow of the type generated by an overhead predator using their cercal sensillae,12,13 and special- ized mechanical organs in the leg may be used to respond to sound stimuli. SENSORY CAPABILITIES OF THE VIBRISSA SENSORY SYSTEM Different kinds of mammals, ranging from seals to chinchillae, employ long facial hairs (vibrissae) to obtain sensory information. In rats and mice, the lateral posterior surface of the face is covered with an orderly array of rows and arcs of vibrissae that are typically identiﬁed by letters (rows) and numbers (arcs). The longest vibris- sae are located most posterior and are referred to as the macrovibrissae, and smaller microvibrissae are grouped more anteriorly in a dense patch. Although microvibris- sae are likely important for perception,16,17 especially of objects a rat is about to attempt to eat, they have received markedly less study. Because of this, references to vibrissae throughout the chapter will indicate the macrovibrissae only, although many of the observations described below should also apply to microvibrissae. As suggested by the name vibrissa, mammals are capable of performing high- resolution frequency-related tasks with these sensors. With regards to airborne stim- uli, rats can discriminate between different frequencies presented with an oscillating air stream. Rats can also use their vibrissae to discriminate between periodic gratings with a spacing of 1. For this kind of discrimination, two vibrissae, isolated to the same row, were minimally required. THE VIBRISSA RESONANCE HYPOTHESIS Sensory stimuli transmitted through airborne, liquid and solid media interacting with the vibrissae likely generate high frequencies of vibrissa vibration. In the case of the textures employed in behavioral tasks, estimates ranging from 200 Hz to over 1 kHz have been suggested for the rate of vibration generated when a rat sweeps its vibrissae over these surfaces. As described in this chapter, we hypothesize that vibrissa resonance may play a crucial role in frequency-speciﬁc transduction of tactile sensory information.
A quick bedside test for viscosity is to allow a drop of fluid to fall from the tip of the needle order procardia 30 mg free shipping coronary heart disease facts. Normal synovial fluid is highly viscous and forms a several- inch long string; decreased viscosity is seen in infection 30 mg procardia fast delivery cardiovascular disease prevalence united states. A mucin clot test (normally forms in < 1 min; a delayed result suggests inflammation) was once a standard test for RA, but is not now routinely performed. Joint fluid is usually sent for: • Cell count and differential (purple or green top tube) • Microscopic crystal exam using polarized light microscopy (purple or green top tube); normally no debris, crystals, or bacteria are seen; urate crystals are present with gout; calcium pyrophosphate in pseudo-gout. Wait until the patient has a relaxed quadriceps muscle because its contraction plants the patella against the femur, making aspiration painful. Insert the needle posterior to the medial portion of the patella into the patellar-femoral groove. The easiest site for aspiration is between the navicular bone and radius on the dorsal wrist. Locate the distal radius between the tendons of the extensor pollicis longus and the extensor carpi radialis longus to the second finger. Make a mark lateral and anterior to the medial malleolus and me- dial and posterior to the tibialis anterior tendon. The subtalar ankle joint does not communicate with the ankle joint and is difficult to aspirate even by an expert. Be aware that “ankle pain” may originate in the subtalar joint rather than in the ankle (Fig. Synovial Fluid Interpretation Normal synovial fluid values and values in disease states are found in Table 13–2. Postinjection flare of joint pain and swelling can occur after steroid injection and persist for up to 24 h. This complication is felt to be a crystal-induced synovitis due to the crystalline suspension used in long-acting steroids. BONE MARROW ASPIRATION AND BIOPSY Indications • Evaluation of unexplained anemia, thrombocytopenia, leukopenia • Evaluation of unexplained leukocytosis, thrombocytosis, search for malignancy pri- mary to the marrow (leukemia, myeloma) or metastatic to the marrow (small-cell lung cancer, breast cancer) T A B L E 1 3 – 2 S y n o v i a l F l u i d A n a l y s i s a n d C a t e g o r i e s f o r D i f f e r e n t i a l D i a g n o s i s * P a r a m e t e r N o r m a l N o n i n f l a m m a t o r y I n f l a m m a t o r y S e p t i c H e m o r r h a g i c V i s c o s i t y H i g h H i g h D e c r e a s e d D e c r e a s e d V a r i a b l e C l a r i t y T r a n s p a r e n t T r a n s p a r e n t T r a n s l u c e n t - o p a q u e O p a q u e C l o u d y C o l o r C l e a r Y e l l o w Y e l l o w t o o p a l e s c e n t Y e l l o w t o g r e e n P i n k t o r e d W B C ( p e r µ L ) < 2 0 0 < 3 0 0 0 3 0 0 0 – 5 0, 0 0 0 > 5 0, 0 0 0 † U s u a l l y < 2 0 0 0 P o l y m o r p h o n u c l e a r < 2 5 % < 2 5 % 5 0 % o r m o r e 7 5 % o r m o r e 3 0 % l e u k o c y t e s ( % ) C u l t u r e N e g a t i v e N e g a t i v e N e g a t i v e U s u a l l y p o s i t i v e N e g a t i v e G l u c o s e ( m g / d L ) A p p r o x. A technician from the hematology lab or BMT facility is necessary to ensure delivery and processing of specimens. Explain the procedure to the patient and/or the legally responsible surrogate in detail, and obtain informed consent. Usually local anesthesia is all that is required; however, in extremely anxious patients, premedication with an anxiolytic or sedative such as diazepam (Valium) or midazolam (Versed) or an analgesic is reasonable. Bone marrow can be obtained from numerous sites, the most common being the sternum, the anterior iliac crest, and the posterior iliac crest. The posterior iliac crest is the safest and usually the site of choice and is described here. Position the patient on either the ab- domen or on the side opposite the side from which the biopsy specimen is to be taken. Identify the posterior iliac crest by palpation and mark the desired biopsy site with in- delible ink. Use sterile gloves and follow strict aseptic technique for the remainder of the procedure. Prep the biopsy site with sterile povidone–iodine solution and allow the skin to dry. With a 26-gauge needle, administer 1% lidocaine solution intradermally to raise a skin wheal. Then, with the 22-gauge needle, infiltrate the subcutaneous and deeper tissues with lidocaine until the periosteum is reached. At this point, advance the needle just through the periosteum and infiltrate lidocaine subperiosteally. Infiltrate an area ap- proximately 2 cm in diameter, using repeated periosteal punctures. Insert the bone marrow biopsy needle through the skin incision and then advance with a rotating motion and gentle pressure until the periosteum is reached. Once it is firmly seated on the periosteum, advance the needle through the outer table of bone into the marrow cavity with the same rotating motion and gentle pressure. Generally, a slight change in the resistance to needle advancement signals entry into the marrow cavity.
Individual Agents Osm otic Diuretics M annitol O sm otic diuretics owe their effects to the physical re- M annitol (O sm itrol) is a six-carbon sugar that does tention of ﬂuid within the nephron rather than to direct not undergo appreciable m etabolic degradation order 30mg procardia with visa blood vessels and the renal calices are located in the. These com pounds not absorbed from the gastrointestinal tract and there- 21 Diuretic Drugs 251 fore m ust be given intravenously order procardia 30 mg with amex cardiovascular week. It should not be confused with isosorbide dinitrate, an M annitol is particularly useful in clinical conditions antianginal drug. M annitol is USES OF DIURETICS useful in m aintaining kidney function in these condi- The ability of certain drugs to increase both ﬂuid and tions, since even at reduced rates of ﬁltration, a sufﬁ- electrolyte loss has led to their use in the clinical m an- cient am ount of the sugar m ay enter the tubular ﬂuid to agem ent of ﬂuid and electrolyte disorders, for exam ple, exert an osm otic effect and thus continue urine form a- edem a. H owever, if circulatory failure is profound and ated with edem a, the com m on factor is alm ost invariably glom erular ﬁltration is severely com prom ised or absent, an increased retention of Na. The aim of diuretic ther- not enough m annitol m ay reach the tubules to be effec- apy is to enhance Na excretion, thereby prom oting tive. This net Na (and ﬂuid) loss leads down m ight otherwise be expected aids in preventing to contraction of the overexpanded extracellular ﬂuid kidney tubular dam age. D iuretics m ay have considerable value in reducing the The m ajor characteristics of the renal response to edem a associated with congestive heart failure; how- m annitol diuresis include a fall in urine osm olality and ever, each patient m ust be evaluated individually, since a decrease in the osm olality of the interstitial ﬂuid of diuresis is not considered m andatory in all patients. The quantity of urine form ation and D igitalis and salt restriction m ay be sufﬁcient to de- Na excretion is generally proportional to the am ount of crease the associated sym ptom s of pulm onary conges- m annitol excreted. In patients who require a di- tion of proxim al water reabsorption, the effects of m an- uretic as adjunctive therapy, the usual choice should be a nitol on proxim al Na reabsorption are not m arked. This is tol adm inistration are headache, nausea, vom iting, chest true especially in m ild congestive heart failure. Too rapid an adm inistration of m ore efﬁcacious com pounds probably should be re- large am ounts m ay cause an excessive shift of ﬂuid from served for those who fail to respond to one of the thi- the intracellular to the extracellular com partm ent and azides. The prim ary use of anhydrous glycerin (O phthalgan) is as an osm otic agent that is applied topically to reduce Hypertension corneal edem a. O rally adm inistered glycerin (G lycerol, O sm oglyn) is used to reduce intraocular pressure and The use of diuretic drugs, either alone or in com bination vitreous volum e before ocular surgery. D iuresis and restriction Urea of salt intake are often sufﬁcient for all hypertensive pa- The use of urea (Ureaphil, Urevert) has declined in tients except those with severe, m alignant, or com pli- recent years owing both to its disagreeable taste and to cated hypertension. Because of its po- a reduction of plasm a volum e with a consequently di- tential to expand the extracellular ﬂuid volum e, urea is m inished cardiac output. H owever, after a few weeks, contraindicated in patients with severe im pairm ent of the initial degree of extracellular volum e reduction is renal, hepatic, or cardiac function or active intracranial not m aintained, probably owing to a gradual increase in bleeding. Isosorbide (Ism otic) is an orally effective, osm oti- A lthough the arterial pressure in hypertensive pa- cally active drug that is m ost com m only used for the tients is related to intravascular volume, the changes in 252 III DRUGS AFFECTING THE CARDIOVASCULAR SYSTEM plasma volume are primarily caused by alterations in to- sure. It appears quite plausible that all of the hypoten- tial space, and this com prom ises gas exchange, dim in- sive effects of the diuretics can be attributed to some as- ishes total lung gas volum e, and increases airway resist- pect of Na depletion, that is, either directly on ance. W ith acute pulm onary edem a of cardiac origin, the extracellular ﬂuid volume or perhaps indirectly through traditional treatm ent has included adm inistration of the the effects of Na loss on autonomic nervous function efﬁcacious, rapidly acting loop diuretics. The this com bination becom es even m ore apparent when it problem s of excessive ﬂuid and K loss indicate a con- is realized that nondiuretic antihypertensives (e. Increased Intracranial Pressure A rise in intracranial pressure results in the appearance Hepatic Ascites of a num ber of sym ptom s, including headache, vom it- Cirrhosis and other liver diseases m ay result in the for- ing, edem a of the optic discs, changes in vital signs, and m ation of excessive am ounts of ﬂuid in the abdom en possibly death. The prim ary causes of ascites are usually ele- of diuretics, can help lower the pressure, particularly if vation of pressure in the portal vein and a decreased the elevated intracranial pressure is of a nontraum atic am ount of hepatic plasm a protein production. The parenteral adm inistration of a hypertonic so- tors tend to reduce the ability of the vascular com part- lution of one of the osm otic diuretics, urea or m annitol, m ent to retain ﬂuid. The tribute to decreased appetite and respiratory oral adm inistration of glycerol also has been used in difﬁculties, am ong other sym ptom s. W hen these sym p- neurosurgical procedures when increases in intracranial tom s are present, careful reduction in the ﬂuid volum e pressure are anticipated. Since patients with cirrhosis vary widely in their re- Renal Edem a sponse to diuretics, conservative initial diuretic therapy Nephrotic Syndrome is called for. The m ainstay of treatm ent, however, rem ains Nephrotic syndrom e is characterized by proteinuria and restriction of dietary Na. The re- with cirrhosis is decreased glom erular ﬁltration, despite sulting fall in plasm a protein concentration decreases the increase in total blood volum e caused by the exten- vascular volum e, which leads to dim inished renal blood sive pooling of blood in the splanchnic vessels. This in turn causes secondary aldosteronism char- D im inished renal perfusion leads to increased aldos- acterized by Na and water retention and K depletion.