经诊以平旦者。阴气未动。阳气未散。饮食未进。经脉未盛。络脉调均。气血未乱。故乃可诊有过之脉。
经人一呼脉自动。一吸脉自动。呼吸定息。脉五动。闰以太息。命曰平人。按一呼一吸为一息。脉四动。然呼吸之
间。必有一息长者。谓之太息。犹岁月之有闰。故脉五动。四动五动。平脉也。若三动则为不及。六动则为太过。皆病
脉也。难经曰。呼出心与肺。吸入肾与肝。按呼吸之气。系卫气。吸非吸入。乃吸起也。盖卫气出下焦。而主之于肺。
肺自下焦吸起。而呼出于鼻。一呼一吸。卫气流行。昼夜循环。周而复始。故气譬则火。火之气。不通则不发。人之气。
不通则病。呼之气。犹火之气出而不入者也。难经呼出心与肺。吸入肾与肝之说似误。
崔紫虚四言脉诀。脉有七诊。曰浮中沉。上下左右。消息求寻。按初持脉轻手于皮毛间。候其表。曰浮。次稍重手
于肌肉间。候其半表半里。曰中。次重手按至筋骨间。候其里曰沉。上谓上部。下谓下部。左谓左三部。右谓右三部。
合为七诊。又经有七诊。谓独大。独小。独疾。独迟。独寒。独热。独陷下也。
四言脉诀。又有九候。举按轻重。按轻下指曰举。重下指曰按。寸关尺。每部有浮中沉三候。合为九候。又经有九
候。脉经曰。九候者。每部中有天地人也。按经所谓天地人。另指头与手足三部之动脉。不指寸关尺也。
经持脉有道。虚静为保。（内虚则心不纷。外静则心不扰。）春日浮。如鱼之游在波。（浮非浮脉。乃浮起也。春日阳
气升。其脉浮起然如鱼之在波。虽浮起而不甚浮也。）夏日在肤。泛泛乎万物有余。（夏日阳气盛。万物有余。故其脉浮
大在肤。）秋日下肤。蛰虫将去。（秋日阳气降。蛰虫将去。故其脉渐沉而下肤。）冬日在骨。蛰虫周密。君子居室。（冬
日阳气伏。蛰虫周密。君子居室。故其脉亦沉而在骨。）知内者。按而纪之。（脉合内之脏腑。其盛衰按脉而纲纪之。是
谓知内。）知外者。终而始之。（四时阴阳之气。终而复始。以脉之阴阳。合四时之阴阳。是谓知外。）此六者持脉之大道。
《内经》规定诊脉要在清晨进行。此时阴气尚未扰动，阳气尚未耗散，饮食尚未摄入，经脉之气尚未充盛，络脉之气调和均匀，气血运行未受干扰。因此，这时才能诊断出异常的脉象。
《内经》说：人一呼，脉搏跳动一次；一吸，脉搏跳动一次。在一呼一吸之间（称为一息），脉搏跳动五次，偶尔因深长呼吸（太息）而增加一次，这被称为“平人”（健康人）。按照一呼一吸为一息计算，脉搏通常跳动四次。然而，在呼吸之间，必然有一次较长的呼吸，称为“太息”，就像岁月中有闰月一样，所以脉搏有时跳动五次。脉搏跳动四次或五次，属于正常的平脉。如果只跳动三次，则属于脉率不及（过慢）；如果跳动六次，则属于脉率太过（过快），这些都是病脉。
《难经》说：“呼气时气出于心与肺，吸气时气入于肾与肝。”按呼吸之气来看，主要关联的是卫气。这里的“吸”并非指吸入外界空气，而是指气的升提启动。因为卫气产生于下焦，由肺所主宰。肺气从下焦升提启动，然后通过鼻子呼出。一呼一吸之间，卫气流行全身，昼夜循环，周而复始。所以气好比火，火的气机不通畅就不能燃烧，人的气机不通畅就会生病。呼出的气，就像火的气向外发散而不向内收敛一样。《难经》中关于“呼出心与肺，吸入肾与肝”的说法似乎有误。
崔紫虚的《四言脉诀》中提到脉有七种诊法：即浮、中、沉，以及上、下、左、右。通过仔细审察来寻求脉象。初持脉时，轻手置于皮毛之间，以候察表证，称为“浮”；稍加重手置于肌肉之间，以候察半表半里之证，称为“中”；再加重手按至筋骨之间，以候察里证，称为“沉”。“上”指上部，“下”指下部，“左”指左手三部脉，“右”指右手三部脉。合起来为七诊。另外，《内经》中提到的七诊，是指脉象单独表现为大、小、疾（快）、迟（慢）、寒、热、陷下（沉伏不起）的情况。
《四言脉诀》中又提到九候：举和按的轻重变化。轻手下指称为“举”，重手下指称为“按”。寸、关、尺每部都有浮、中、沉三候，合起来为九候。另外，《内经》中的九候，据《脉经》记载，是指每部中包含天、地、人三候。这里所说的天地人，另指头部、手部、足部三个部位的动脉，并不指寸、关、尺三部。
《内经》说持脉有一定的法则，以内心虚空宁静为根本保障。（内心虚空则心神不杂乱，外表安静则心神不受干扰。）春季脉象浮起，像鱼在水中游动。（这里的“浮”不是指病理性的浮脉，而是指脉气浮起。春季阳气上升，脉气随之浮起，如同鱼在波浪中游动，虽然浮起但不过分浮越。）夏季脉象在皮肤表面，泛泛然如万物生长旺盛有余。（夏季阳气旺盛，万物繁茂有余，所以脉象浮大且在皮肤表层。）秋季脉象下沉至皮肤之下，像冬眠的昆虫准备藏匿。（秋季阳气下降，冬眠的昆虫即将藏匿，所以脉象逐渐下沉并位于皮肤之下。）冬季脉象在骨骼深处，像冬眠的昆虫严密包裹，君子安居室内。（冬季阳气潜藏，冬眠的昆虫严密包裹，君子安居室内，所以脉象也深沉而在骨骼处。）懂得内在脏腑的人，通过切按脉象来纲纪其盛衰情况。（脉象与内在脏腑相合，根据脉象的盛衰来梳理脏腑状况，这就叫作“知内”。）懂得外在四时变化的人，能洞察阴阳之气的终始循环。（四时阴阳之气终结后又重新开始，将脉象的阴阳属性与四时的阴阳变化相合，这就叫作“知外”。）这六点就是持脉的大道。
The *Classic of Internal Medicine* (*Huangdi Neijing*) stipulates that pulse diagnosis should be performed in the early morning. At this time, Yin Qi (Yin Energy) has not yet been disturbed, Yang Qi (Yang Energy) has not yet dissipated, food and drink have not yet been ingested, the Qi of the meridians is not yet abundant, the collaterals are harmonious and balanced, and the flow of Qi and Blood is undisturbed. Therefore, it is possible to diagnose abnormal pulses at this time.
The *Classic of Internal Medicine* states: With one exhalation, the pulse beats once; with one inhalation, the pulse beats once. Within one full respiratory cycle (referred to as one "Xi" or breath), the pulse beats five times. Occasionally, due to a deep sigh-like breath (Tai Xi, 太息), it may beat six times. This is referred to as a "Ping Ren" (Normal/Healthy Person). According to the definition where one exhalation and one inhalation constitute one "Xi," the pulse typically beats four times. However, between respirations, there is invariably one longer breath, called "Tai Xi," analogous to a leap month in a year. Thus, the pulse may beat five times. A pulse beating four or five times per respiratory cycle is considered a normal Ping Mai (Normal Pulse). If it beats only three times, it indicates insufficient rate (bradycardia); if it beats six times, it indicates excessive rate (tachycardia). Both are Bing Mai (Pathological Pulses).
The *Classic of Difficult Issues* (*Nan Jing*) states: "Exhalation relates to the Heart and Lung; inhalation relates to the Kidney and Liver." Regarding the Qi of respiration, it primarily concerns Wei Qi (Defensive Qi). Here, "inhalation" does not refer to the intake of external air, but rather to the initiation and rising of Qi. Since Wei Qi originates from the Lower Jiao (Lower Burner) and is governed by the Lung, Lung Qi rises from the Lower Jiao and is exhaled through the nose. Through each exhalation and inhalation, Wei Qi circulates throughout the body, cycling day and night continuously. Therefore, Qi can be compared to fire: if the Qi of fire is blocked, it cannot burn; if human Qi is blocked, disease arises. Exhaled Qi is like the outward emission of fire's Qi, which does not return inward. The theory in the *Nan Jing* regarding "exhalation relating to the Heart and Lung, inhalation relating to the Kidney and Liver" appears to be erroneous.
Cui Zixu's *Four-Character Pulse Mantra* (*Si Yan Mai Jue*) mentions seven diagnostic methods for the pulse: Floating (Fu, 浮), Middle (Zhong, 中), Deep (Chen, 沉), Upper (Shang, 上), Lower (Xia, 下), Left (Zuo, 左), and Right (You, 右). One must carefully examine and seek these positions. Initially, when holding the pulse, light pressure is applied at the level of the skin and hair to observe exterior conditions, called "Floating." Slightly heavier pressure is applied at the muscle level to observe half-exterior/half-interior conditions, called "Middle." Heavier pressure is applied down to the bone and tendon level to observe interior conditions, called "Deep." "Upper" refers to the upper position, "Lower" to the lower position, "Left" to the three positions on the left hand, and "Right" to the three positions on the right hand. Together, these form the Seven Diagnoses. Additionally, the *Classic of Internal Medicine* mentions another set of Seven Diagnoses, referring to pulses that are exclusively large, small, rapid (Ji, 疾), slow (Chi, 迟), cold, hot, or sunken/depressed (Xian Xia, 陷下).
The *Four-Character Pulse Mantra* also mentions Nine Positions (Jiu Hou, 九候): the variations in lifting and pressing pressure. Light finger pressure is called "Ju" (Lift/Raise, 举); heavy finger pressure is called "An" (Press, 按). Each of the Cun (Inch, 寸), Guan (Bar, 关), and Chi (Cubit, 尺) positions has three levels: Floating, Middle, and Deep, totaling nine positions. Furthermore, the Nine Positions in the *Classic of Internal Medicine*, as stated in the *Classic of Pulse Diagnosis* (*Mai Jing*), refer to Heaven, Earth, and Human within each position. Here, "Heaven, Earth, and Human" refer separately to the arterial pulses of the head, hands, and feet, not to the Cun, Guan, and Chi positions.
The *Classic of Internal Medicine* states that there is a proper method for pulse diagnosis, with inner emptiness and outer tranquility serving as the fundamental guarantee. (Inner emptiness prevents mental clutter; outer tranquility prevents mental disturbance.) In spring, the pulse floats, like a fish swimming in waves. (Here, "floating" does not refer to the pathological Floating Pulse, but to the rising nature of the pulse. In spring, Yang Qi ascends, causing the pulse to rise slightly, like a fish in waves—rising but not excessively floating.) In summer, the pulse is at the skin surface, abundant and flourishing like all things in growth. (In summer, Yang Qi is abundant, and all things flourish; thus, the pulse is floating, large, and located at the skin surface.) In autumn, the pulse sinks below the skin, like hibernating insects preparing to hide. (In autumn, Yang Qi descends, and hibernating insects prepare to conceal themselves; thus, the pulse gradually sinks and lies below the skin.) In winter, the pulse is at the bone, like hibernating insects tightly wrapped, and the gentleman stays indoors. (In winter, Yang Qi hides, hibernating insects are tightly wrapped, and the gentleman stays indoors; thus, the pulse is also deep and located at the bone.) Those who understand the internal [organs] press the pulse to catalog its excesses and deficiencies. (The pulse corresponds to the internal Zang-Fu organs; observing the pulse allows one to organize the status of these organs, which is called "Knowing the Internal.") Those who understand the external [seasons] perceive the beginning and end [of cycles]. (The Yin-Yang Qi of the four seasons ends and begins anew; by correlating the Yin-Yang of the pulse with the Yin-Yang of the four seasons, one is said to "Know the External.") These six principles constitute the great way of pulse diagnosis.